Reminds me of the AlphaGrip[0] somewhat. Of the problems of using it, I mean. I bought it like 10 years ago, and sold it a couple of years later, it's good to see that they're still in business.

On the AG, instead of a combination of buttons to produce a keypress, you have 8 keys (buttons?) that can rock in two directions, plus thumb buttons, including red and green "shifts" that work as Fn keys. Normally you type text, pressing red shift you input numbers and arithmetic symbols, with green shift the rest of the symbols. It was great for games and got past my regular QWERTY speed writing English text after a couple of months.

Now, if you write in more than one language, you're screwed. Using other layouts would make the already difficult task for developing muscle memory even more annoying. I tried it with US-Intl layout (as I was used to it on QWERTY) to have a unique layout for multiple languages, but it quickly becomes unusable: to produce an "À", I don't remember exactly, but required 2+2 or 3+2 simultaneous keypresses, plus US-Intl is implemented different in different OS, so sometimes you have to take into account dead keys, sticky keys, sometimes not. And don't get me started on shortcuts and programming...

[0] http://www.alphagrip.com/