I got my Hitbox earlier this week, transitioning from gamepad. Here's my story:
Movement so far is a bit weird, and I've forgotten that the 8 button even exists a few times. Diagonals are not hard to hit at all. Special movements (e.g. α 236236236/214214214) take a slight amount of relearning but you can get that down within a half hour.
Half Circles (Astaroth, Algol) are extremely consistent now, as none of them require diagonals and all it takes is a simple swipe of the finger in either direction. My grabs with Astaroth are almost always JF grabs.
agA is something I have to relearn entirely from scratch. It honestly feels like I've never done the move before, and I'm pretty much starting over on it.
iFC A+G*B+G is extremely fast for me now, on par with my SC4 speed (I lost some speed because of the new buffering system)
iGDR is much more consistent on Hitbox. I don't even play Cervantes and can get it pretty easily now.
iStab is easier from everything that isn't FC, in which case I seem to have a weird bit of trouble and get something else - usually 6B. On the plus side, I get 236B:4 and 236236B:4 much more consistently now - I almost never got it on pad.
I picked up Ivy and was able to do iCS for the first time in this game on a Hitbox.
Overall, while there aren't gigantic advantages to using Hitbox in Calibur compared to games like Marvel or Street Fighter, it still makes my inputs much more consistent to the point where I believe it's a superior method of input.
EDIT: One thing I forgot. Training Mode is now a bit more cumbersome to get around, because pressing Triangle + Select seems to disable the Hitbox. IDK what's up with that, but it means that you have to navigate Training Mode through the pause menu instead. A small bonus is that you can no longer accidentally change modes by nudging the right stick.