The handheld unit screen design idea is awesome and will have a lot of uses in a lot of games, I can't wait to see some more clever uses come out of this idea. I'm a little concerned about being able to use it on FPS games though, on twichy first person shooters the controler has to fit like a glove and be light weight or your hands will cramp up. FPS games are tense and the difference between a headshot and a miss is extremely tiny, I'm not sure a flat rectangular controller will measure up.
On THOSE games I hope the developers do NOT add a feature that requires the flat handheld because I'll be switching out to my gamer controller for sure.