It took me a few weeks to really get to muscle memory, but after that I disliked full-size keyboards enough that I started using kmonad on my laptop with the traditional keyboard. I eventually ended up with kanata (which has a superior chord handling) everywhere, until I got a piantor 50%, when I switched to QMK.

I switched by degrees, though; I'd used a more limited set of layers for a couple of years before going full gonzo, so I was used to the modality; adding more layers was less a new paradigm and more just adding complexity to what I was, by then, familiar with. So I can't say I'm a fair measure.

QMK has been a struggle to get all of the settings working such that there isn't some behavior that is annoying, and I'm still not there, but having the programming in the keyboard has made some situations easier (consoles, etc).

I'm 9 mos into the piantor, and I still struggle with remembering where I bound some infrequently used layers, like the layer I put all the F-keys. And rarely I'll think about how to get a key - rather than relying on muscle memory - and simply fail to remember the magic combo. However, I won't voluntarily go back. Having numbers and special characters accessible without having to change my hand positions is simply invaluable, and I still use kanata on my laptop to get the same behavior, despite it meaning I have a whole row of keys I'm not using anymore.

The biggest hassle in going back to a full size is the reduced number of thumb keys. And I admit, I learned to touch type being able to hit the space bar with either thumb, and simply do not have the luxury of enough keys to dedicated to duplicate functions to allow this. This would be probably my biggest complaint, and only regret about switching.