Yeah I'm definitely not claiming novelty (http://ohbah.com/mods/chairkey/images/cat.jpg). Over the past year I've tried a number of different solutions, and actually alternate among this, a mechanical keyboard and various (optimized) desks (standing and not).

The idea with this is that your arms will be pulled down (as you noted) but into the cushy arm rests, as opposed to your arms supporting themselves (if you are in the proper typing position). And they are tilted so that you end up resting your wrists on the side, as opposed to the bottom of your wrist where your tendons/nerves are most exposed. I don't know much about the science of ergonomics, but my arms do feel more relaxed in this position :).

But yes typing too hard has also been an issue for me in the past, the mechanical keyboard has been a huge help for that. Thanks for the comment!