The following is in no way a request for information regarding the illegal conversion of any firearm.  

After seeing this ad I was reminded of a certain Shotgun News\drop-in autosear for the AR-15, that also seemed drastically under priced. Although the auto connecter in the glock ad is less than 80%, and therfore perfectly legal to purchase. The no refund and lack of detailed description leads me to think these sears are probably a rip-off.
The term buyer beware comes to mind.

www.hessearms.com/nfa.htm

Any thoughts from the peanut gallery?