The top image of this post looks like an RSI nightmare illustration. I’m sure the situation would be better if there was some sort of molded support behind the keys, but even in the linked video you can see the opposing hand holding it in support.
I have a keybow, and it is a great little 12 key board, but I’m not convinced it would be comfortable to type on for long, although chording might improve the matter. However, the fact that it is three rows of four keys, means that the thumb is redundant which is a waste of a useful typing digit.
See also the good, old, yet surprisingly little known Chordite. Some real-world pics: https://www.chordite.com/teensypictures.htm
Wow, I’d never seen this keyboard (?) before! I really like the
idea, even tho the prototypes are a bit..dated.