I may consider on trying out the Mixbox:
*pic*
Seen a lot of Guilty Gear, Tekken, DBFZ players using it.
I... Wow.
That sounds like a great solution for me since when I'm home I play using KB. This would allow me to actually travel and play on any platform without re-learning much.
That said, there are some things I've learned:
Layout of these directional buttons could be good simply because people may be used to it. Otherwise it's not optimal for the reason
@Lulu has mentioned. When I was trying myself at Guilty Gear I had to re-assign keys on my KB to a more hitbox-style layout simply to cope with diagonal super-jumps (down, up while holding left or right). Perhaps, "WASD-like" layout can be viable (although a 3D FG makes it harder to get used to how your "up" button is mapped than 2D does), but keys must have specific shape allowing you to easily slide from a button being held to another one. That's not what most devices allow to do easily enough, and looking at your picture, neither does that one (although that depends; if "down" button doesn't sink too deep when pressed, it could work well - "up" one is shorter, and I guess that's for that very reason).
It is especially felt when you need to use a lot of circular motions that involve "up". It matters in a game like DoA that likes sophisticated inputs for the sake of it.
But then again, DoA5 was quite uncaring to any keyboard/hitbox user. Directional input timings were relatively strict, there were only so many diagonal inputs you could drop, and some characters were constantly peppering you with pointless 360, so... While hitbox layout makes all of that easier to overcome, it still feels more natural to use analog controller for that.
Which, of course, requires even more time to retrain for...