A (not necessary correct):
1. Game have to be programmed to support tracking system. Also, through software you could emulate mouse or joystick to take control of view.
2.
http://en.wikipedia.org/wiki/List_of_games_supporting_FreeTrack
Every list is incomplete...
3. With TrackIR you have uniformed hardware. You don't have to fine tune system for best performance. Developer have obligation to give support.
But... if you have
spare time, any skills with wires and construction, will to read how-to and set-up your own system - FreeTrack is choice for you.