After some days of use, I'm quite happy with this faceU but I discovered a little thing.
If you modify keycode using a text editor (press combo keys for 5s), they won't be updated when you flash a new keymap with hidflashboot (more or less the name).
It's not so disturbing, but I deleted my left control and after that I couldn't go back to the keymapper on text editor, and… it became disturbing.
But don't worry : just create a new keymap with a left control key somewhere you never use keymapper (typically on alphas) and flash this keymap. Doing this you will be able to access keymapper and revert your F*****g mistake.
PS : I post it there because I spend almost two hours fixing this. I hope this could help.