You could just connect your cars with drawbars too.  Or dummy scale couplers from the Jurassic before any kind of operating coupler had been invented, and no one switched at all. These would look really good, not break apart, but be separable for transporting the trains to, and from the exhibit

For what you are doing, the X2F couplers appear to be doing what you need.  You stated a good case for using them in the unusual environment in which you are running your trains.  In all my years of model railroading, though,  this is the first time I've ever seen an advocate for these early couplers over relatively prototypical appearing knuckle couplers.

101 scale miles per hour in a loop at an exhibition for children is different than a seriously operated model railroad with train make-up, interchange set-out and pick-up, customer switching, local freights working communities enroute, and at the final destination, breaking up the train, switching the interchange on that end, customer service, etc.  in this setting the X2F will never work well, virtually unable to uncouple without picking the cars up. I know, I used to have them and wildly celebrated the day the last ones came off the railroad.

If you merely running trains continuously, not uncoupling your cars, and can't see the couplers, you don't need realistic ones, you don't need ones that look good. But, as soon as you start moving cars independently of permanently, coupled trains, most modelers want to see a coupler that has at least some prototypical appearance.

I do have to say that sagging couplers can be corrected by more careful installation. A Kadee coupler gauge tells all.  But you have to use it. Some cars need more work than others or may need a more specialized coupler, Kadee makes dozens.  Plus, I can't imagine Kadee couplers breaking unless some kind of inordinately hard usage is happening.  If you are running 100 car trains at 101 scale miles an hour and stopping them dead within an inch, the weight of the sudden slack action probably will break couplers.  Imposition of astronomical toy train level demands on a fine scale product will probably cause failure.  Kadees aren't made with this in mind.

My last comment is about train speed. The clubs I've been in, when open to the public, all the children complained the trains are too slow, and aren't happy until they are running at rockets speed. We use that as a teachable moment to tell them that in the Railroad age, Trains did not run that fast, we are trying to present a relatively historically accurate  operation. Most of them will accept that when you tell them. Railroad history is little known and obscure enough already without perpetuation of unrealistic images.

1. DC steam locomotives back in 1960 all had one wire to the tender. The engine would pick up on one rail, the tender would pick up on the other.  The first HO steam locomotive I ever saw back then was a Varney Casey Jones. It had that one wire to the tender and I thought it was the neatest looking thing I ever saw, just like the hoses on the steam engines that I had seen only a couple of years earlier on the T&NO back home. The several wires on today's DCC steam locomotives can push the tender wrongly to one side or another or pick it up slightly off the rail, causing a derailment. Some are easier to cure than others. I've had a couple of tough customers. When you get them right, they can approximate the numbers of hoses that connected steam locomotives to their tenders.

2.  Geeper, I would think very long and hard before investing much in TT scale trains. Unless things have changed, there just is not the availability of just about anything that HO has.  I'm thinking more of supplies and ancillary items like trackside details, signaling, structure kits, decals, and so on. You've probably looked at it harder than I have, but I have a feeling that going into a marginally popular scale like that, one will be constantly looking on eBay for old HP products items.  And wishing that you could get stuff that can easily be had in more popular scales. Plus, if you're getting up in age like me it's just really hard to see those smaller trains. I restarted Model Railroading 15 years ago after being out for 40. The few HO items I had saved from way back in high school days had burned up in a house fire, so I could've started in N scale from ground zero, and I thought real hard about it.  HO won out for all the reasons listed above, and I've never regretted it. Plus, a friend of mine with considerable experience in the small scales says that operation can be very tenuous with low tolerance for only slightly unclean track and such. Plus the little cars are so light that realistic switching is almost impossible, smooth coupling up just cannot be had. Switching was going to be a major part of the branchline I had always wanted to build, so that pretty much sealed the deal to go to HO. I have never regretted it.  Even though I could've had twice the railroad in my space, it would've never operated to my satisfaction.

You need smaller steam engines for workaday purposes. 

When I first started my present layout, about 15 years ago, I knew it was going to be a branchline from the beginning. I told myself, I will never get an engine larger than a 2–8 – O. Then, I joined the club with an extremely large layout, having a mainline run of over 700 feet with several steep grades and curves. I bought a 4–8–2 to run on that layout, then four mikados. Then a couple of pacifics. Naturally right after I bought the Pacifics, the last ones of the bunch, the club closed and was torn down.  The only place left to run them was at home. And I rarely do it, because of the cabs hangover too far when going around certain curves and through sharp switches. I do use them as switchers in the yards on either end because supposedly that is mainline trackage where my branch intersects to go out Into the backwoods. But their days of hauling 40 and 50 car freights are over.

I have a variety of consolidations, 10 wheelers, and decapods to work the actual railroad. But, really, the only ones to get a consistent workout are the decapods ...... penultimate short line locomotives if there ever was one. And they've always been a favorite of mine since I saw a photo of one of them working on the MP back in the 40s near Baton Rouge Louisiana.

1.  Your Berk is an aftermarket repaint. Hopefully they didn't trash the whole engine with a lousy job.

2. pick ups on the tender only are not so good. The engine might start stalling on unpowered switch frogs and and places where some gnat left a calling card on the rail.

3. Never heard of an HO scale steam engine that actually emitted steam from places like cylinder cocks and pop valves. I have seen videos of it on very large scale engines, but they were very large, almost to where they could've been actual live steam engines.

Geeper, I started limiting the use of longer-than-40' cars on my relatively small layout quite a while back, even though I have a good population of really nice 50-foot cars.  My layout is a branchline about 50 feet long with an interchange point on either end. There's the interchange track, a run around track a two track yard that holds about five cars each, and a couple of ag branch type customers like co-op warehouses, and oil dealers. Nothing to excite mainline enthusiasts, but running between those two terminals, if you can call them that, and set-outs/pick-ups at rural settlements out on the line can take hours. But, the rub is that there's room for only about 35 40-foot cars on the layout to operate well. After that it's too crowded. And even less if the rural open space that I strive for begins to be compromised. A couple of 50 foot cars can really eat into limited space.

One car I really miss running is a string of 50-foot wood express reefers like we used to see in strawberry country in southeast Louisiana, spotted at almost every team track along the Illinois central between Baton Rouge and Hammond.  I have a bunch of those cars, but they really eat up my track if I have more than a couple of them on there at once.

And I can't even think of my complete head-end heavyweight passenger train I ran with my MP 4–8–2 on the now long-gone club.  Maybe one day....

HP products is still in business:

https://www.hp4stamping.com/history/

Just not the model railroad business

Apparently there's a forum for H P Products TT scale-

https://www.ttnut.com/viewforum.php?f=22

"Crude" wasn't the right description of the paint job on the brass SSW long caboose.  It's very cleanly done. It's just a little, well, bright. A little too Crimson to match the SSW color. Nothing that a little weathering powder wouldn't tone down.

I have a second one that is more correctly painted. When I saw it in the glass display case at the LHS, it was correctly lettered.  When I got home, I saw that the previous owner had only lettered one side of the car. Why, who knows. I just keep that side of the car facing to the outside of the layout. Maybe one day I'll fix the other side.

Quentin, excellent reading.

https://www.amazon.com/Cotton-Belt-Engineer-Standefer-1898-1981/dp/1449069207

Trivia:  What cellphone company did the SP jumpstart?

Right on, Len

Wait until you get into the motor control cv's.  Those babies will crawl like ants!

One last comment is related to the expense of metal knuckle couplers. It appears that they only are used as stock items on very expensive premium – quality ready to run cars with separately applied ladders and complete underbody brake rigging. These kind of cars can run up to $50 or $60 each, are very fragile, and generally purchased only by very experienced (and affluent) model railroaders.  I have a few. They are very beautiful, but I found them to be so fragile that I don't use them in day-to-day operation very much.

The plastic knuckle coupler market arose when Kadee's patents ran out years ago. The premium ready to run market did not exist yet, and plastic ready-to-run low- to mid- quality cars came with what were called X2F couplers, or erroneously "NMRA" couplers. They were terrible in every aspect, and the plastic knuckle couplers that eventually arose were a major improvement,, despite their lack of durability and lack of smooth operation characteristics.

I used to assiduously and immediately replace every non-Kadee coupler on new pieces I bought with Kadees. At this point in time, I'm a little slower doing it, but the less than spectacular operation of non-Kadee couplers makes me eventually get around to it.

DCC appears to have nothing to with track switches.  Other than a switch motor that might operate via an address in the same manner as a a locomotive.

I have a DCC layout.  I have track switches with both insulated frogs and powered frogs.  DCC has no bearing on train operations over either type of switch.  I believe the term DCC turnout is a misnomer and a marketing term.

A jumper wire from the good rail to the bad rail.

Seeing a discussion about TT scale model railroading is like finding ancient scrolls, long undiscovered laying in a cave somewhere. I haven't heard any mention of it since the 60s when I first started in this hobby. It basically was the brain child of one man, Hal Joyce, long deceased. I believe his company was called HP products, but I'd have to confirm. I don't know if anyone else ever really made much in that scale. It never really caught on. It wasn't really that much smaller than HO, maybe 15% or so. In reality, you had to go a lot smaller, like N scale, to begin to make much of an impact. I believe that the time of its creation, TT scale was about a small as you could make a model and get a motor inside of a locomotive to make it actually operable. Later miniaturization led to N scale, significantly smaller than HO scale with a corresponding increased ability to model in limited space.

I am curious, and would like to hear, how you even heard of TT scale, what got you into it, what equipment you were coming up with, and anything else about it. It really is a Backdraft from the Model Railroad Jurassic.  If there is renewed chatter about it on the Internet, it's news to me, I thought TT scale was long dead.