Evolutionarily it would't make sense if the human body wasn't 'self-contained' - requiring no external tools to work comfortably.

Your normal posture is to have the arms relaxed, or with a moderate amount of tension by keeping them lifted a reasonable amount of time, and variating the posture as well.

A well-developed hunter/gatherer would definitely have arms strong enough to type this way without getting particularly tired.

So what we modern humans ought to do is to keep the arms strong (by exercising), and to not compensate tiredness with artificial mechanisms.

I'm aware that this argumentation is somewhat dubious (and probably I failed to express it properly), but as a simpler experience report, I've worked this way 4+ years without trouble. First days will suck though.