I have one of these I use on my 9mm and 223 AR's. I have some videos on youtube of my 9mm in action. I love it and it works great. Virtually a select fire for only $350 and you don't need a $200 tax stamp.
I'm trying to get it to work on one of my 22LR AR's, but so far no luck. Not enough umph to make it work.
You can find my vid's by looking for my ID -steel609