It looks really awkward to me. I know that when I get into a game I kinda fight with the controller. You know, body language. I'd think that having it separate like that would be, well, awkward.

Also, sometimes when I use the controller and I'm pushing with my thumb, I'm not really pushing against the same hand, but using the same hand as the fulcrum and pushing against the opposite hand. Having to provide the moving and stabilizing force with one hand seems like an invitation to bad cramping.