As far as them being legal, I hope they're not.

Yeah they may kick ass to play with, but it just gives the bad people in the world a head start. You shoot a gun in a mall, most of the mall is going to hear it and freak out, and he will be easily seen. You shoot a silenced gun in a mall and only a small amount of people hear. Hard to explain what the hell I'm talking about..
Oh and I would be scared to test a silencer.. not so sure I want something that could interfere with a bullet moving 2500fps in my hands.

