I have one, but didn't get a chance to use it this year because I bought it late in the season, then I was coyote hunting all the time instead of crow hunting.
I have seen videos on youtube of them in action and it looks like they work. Crowbusters has a electronic decoy that it similar. Most people claim that any movement in your spread will really help.
If you want one, you better hurry, because they are discontinued.