I don't really have an issue with different sized keys... Heck, I got started on accordion as well as piano!

I guess my main problem is when I'm forced to mix and match. For me, at least, I have considerable problems playing TWO keyboards with different widths or depths. Especially when stacked, and both hands have to adjust. As long as it's just the one, most of us can adjust, but when you are constantly going from one to the other, it forces you to stare down a lot, or concentrate extra hard as you swap keyboards.

YMMV