I already have RSI from keeping my hand in that position for too long.

i would like to borrow it for a week to play with it. Nice to see some changes ;D Never ever touched something like that. Please report your opinion about this mouse if it'll happen that you own it.

It looks interesting. MS guys have tried something similar with Natural Mouse 6000, but it wasn't successful. You can get comfortable mice from many companies; for me Razer DeathAdder, Logitech G700 and old MS 6000 shapes were really great - in general non-claw grip is ok; pair it with soft mouse pad and exercise (for example a set from Day[9] #252) from time to time and you'll be ok.