So for me at least it's pretty quick. Having radically different keyboard layouts is actually helpful because it's really clear (to your muscle memory) that you're doing something very different.
I use the ErgoDox that I built from plans I found online, a MS Natural Ergonomic 4000, my laptop keyboard, and rectangular Dell keyboards for random computers at work.
If you've got the time/money and it looks interesting I'd encourage you to try it. If it works out you'll be happy, and if doesn't you'll at least know that it doesn't work for you. But hey, it's your choice, for sure :)
I'd probably adapt in a similar fashion. I guess I'm off to keyboard shopping now.
An unexpected side effect is I actually type a lot better on my laptop's keyboard now because the Kyria encouraged me to use all of my fingers (my ring fingers were almost never used before). I don't type noticeably faster, just much more comfortably.
I have much bigger problems switching between dvorak and qwerty on either keyboard, to the point where I'm considering properly relearning qwerty despite being fluent in dvorak over a decade.
Aside from that, transitioning takes no more than half a minute for it to feel natural again.
Now my only issue is that I accidentally hit caps-lock a lot on other keyboards as that is mapped as backspace normally, but otherwise still fast and accurate.
I do find that I get those wrong a bit when I switch back to the laptop.
Oddly, never a problem with tab and return, the main thumb keys (besides space, which doesn't change), although I really miss "delete back one word" which is my fourth large thumb key. Alt-backspace is just not the same.
Switching back to a normal staggered layout doesn't take long for me, but I wouldn't like doing it every day.
Do people using these keyboards as their daily driver have trouble adapting to normal keyboards they need to use from time to time.
I suppose I could try one and find out if it's an issue for me, but I'd be worried I get deep into this rabbit hole only to find I'm useless if I have to work on something on some other machine.