I almost always use a split keyboard when I'm able to set up a stationary environment. But I love to go mobile: coffee shops, beaches, couch, bar counters. I never forget how to use a normal keyboard, nor do I lose any speed. That might be the trick, maybe you need to switch between the two occasionally.

I'm using UHK for almost a year and can share with my experience.

It really depends on a keyboard - if it is similar to regular one or not. The UHK is pretty similar to regular keyboard - keys are staggered (not ortholinear), there are no additional thumb keys which are also not available on a regular laptop keyboard. After a year with UHK I'm still able to jump between laptop and UHK when needed. Somehow muscle memory "detects" when my hands are on UHK and I start using additional shortcuts which are not available on laptop.

Meanwhile if you'd pick something like Dactyl https://github.com/adereth/dactyl-keyboard, I believe it would be more difficult to jump arround.

P.S. After a year my typing speed on split keyboard is higher compared to laptop.

I’ve been using an Atreus split ortholinear keyboard with the Colemak layout for more than a year now, and I have no difficulty switching back to a standard Qwerty staggered keyboard when I use my laptop or someone else’s computer.

I've been on an ortho (Let's Split) and a vertical staggered board (Iris) for a few years now. The Iris is stuck in my locked office that we can't go back into for the foreseeable future so I'm on the Let's Split (with pedals!) at home. Honestly I think I still type faster on a Macbook Pro keyboard, and that's the one that everyone hates. I'm plenty fast on the ones I built myself, but still just fine on that one. The big thing is that I will sometimes reach for a layer combo that isn't there on the MBP. It's very rare, since I think the staggered layout mostly hits my muscle memory preventing that, but it can happen that I'll almost hit a nonexistent chord on it. Never actually typed them out that I can remember though.

My desktop has a split keyboard and I switch between that and the laptop's normal one pretty effortlessly. Even all the shortcuts just come.

However, after not using my Das keyboard for a few weeks, I found that I couldn't type with it at all any more. I realized later that that's because the distance between the keys is smaller, so after I realized that and compensated, it became easier to type there. I never use it, though, so I haven't put in any effort.

I've been doing most of my typing on an Ergodox for years and while switching to a "normal" keyboard feels clunky and a bit awkward I can still type reasonably well on those. I guess it just becomes a lot more obvious how un-ergonomic those are (especially for the left hand in my experience). Having to bend your hand in weird ways to hit the modifiers feels odd when you're used to have them fall naturally below your fingers.

I've been using an Ergodox EZ for a lot of professional work for a few years now, but since I'm bouncing between that and laptop keyboards regularly, I haven't found any issues switching between layouts. I do occasionally try to use some custom-mapped ergodox keys the wrong way on a laptop keyboard, but it's a momentary embarrassment and not a thing that impedes my work.

It took a few months, not years, for me.

I don‘t mind it. 99% of my time spent typing happens at my own desk(s) and the few times I use someone else’s keyboard don‘t justify compromising on comfort with my own setup.

A big part of what makes it hard for me to use a normal keyboard now, isn‘t so much the physical shape, but the programmability and additional modifier keys offered by the UHK, both of which I use a lot.

I use an Ergodox EZ for most of my typing, and don't really notice any major problems adjusting back to a standard keyboard on the odd occasion I find myself using a laptop keyboard instead. The only exception to that is for the first half hour or so I'll try holding caps-lock to get control, and just get escape being held instead.

I don't find it hard to go back (which I do if I use just my laptop). I do find it reminds me of the weird angle laptop keyboards force my shoulders and wrists into.

not really. I use the kinesis freestyle at my desk 90% of the time, but have no issues with my personal computer at the kitchen table or couch.

after half year on kinesis I started to touchtype on "normal" keyboards. Now, few years in, still no problems.