Most of these keyboards based on the ErgoDox (and the ErgoDox itself) make the mistake of considering that the thumb is a finger positioned like the others. And the keys you're supposed to hit with your thumbs are just placed in a crazy way (totally non-ergonomic IMHO).

To me one of the rare person who really "got it" is "Jesse" (he's both here, on GeekHack and on Deskthority) with its "butterfly" keyboard.

That's one of the only split (and ergonomic) keyboard that takes into account the fact that the thumb's opposition-apposition makes it unlike any other finger.

Look at his "butterfy" keyboard here and how smartly the keys you're to hit with the thumbs are positionned:

http://blog.fsck.com/2013/12/better-and-better-keyboards.htm...