More info on the I-Dong. Not really a competitor to the Kinect

i-dong – Play table tennis in your living room

The i-dong table tennis uses optical tracking technology to capture player’s all movement accurately. Players can do all kinds of shots such as backhand topspin, backspin serves, backspin chop, etc. Thus i-dong ping-pong can simulate a real table tennis match very accurately. The E-fitness device accurately captures players’ position and movement through the tracking identifier on the TV.

Because of this players will find it difficult

Kinect review