I've used a couple phone controllers, and the problem always comes back to no game really supports them because not everyone has one. The best games for a controller are the Modern Conflict games, and even then they have quicktime events that require me to drop the controller and touch the screen.

At the very least 8-bit era emulators will be able to capitalize on them well since those games just require 2 buttons and a D-pad, which a single hand of this controller supplies.