I have used both the FATS system and the AIS ( www.firearmstraining.com
) system to train on. The AIS is by far the better of the two because, as rebel said, it is a real weapon converted to shoot the bullets using compressed air. The weapon is not tethered as it is in the FATS system, allowing you to move and use cover. Also, the computer operator controls a small gun of his own that is attached above the screen. He uses a joystick and laser sight to operate this gun from his position. As he watches the student on a video screen he can use the laser sight to aim at parts of the student not behind cover and can shoot a .68 cal nylon ball with great accuracy. It won't injure but sure does teach a lesson!
However, my opinion is (for what it's worth) you can not beat training with simunitions for the next best thing to reality. Right down to human adversaries, reloading and stoppages this is as real as you can safely get. Besides, it's a hell of a lot of fun!
If not you, then who?