Rating: - Works well with Rock Band on Wii
Bought it so my wife can play rock band with me on the Wii. Hooked it up through wireless and it works great. She can move around the room and it picks up her voice no problem. It is a real microphone and comes with an adapter and wire you can use to plug it into an amplifier or karaoke machine if you were so inclined.
The only downside is that both the wireless transmitter and microphone use batteries and must be switched on when you are ready to play. In addition, you must use the wiimote to join the band and make song selections. So it gets a little cumbersome to setup, but I would think this would be the case with any microphone that wasn't specifically designed for use with Rockband. However I would still definitely recommend it.
Rating: - Poor reception
I really wanted to like this item. I do both Singstar and Rock Band with friends and family and was hoping this would solve the problems inherent in a wired mic (people tripping on it, etc). However, the mics only sometimes seem to work at all with Rock Band, and have a high pitched squealing sound when they do work in either game. It may be different for the Wii, but I can't recommend them to anyone otherwise.