I don't know about Gentry's unit, but I have seen some measured Sound Pressure Level data for the BP Tec that showed it was not louder. They have some theory of operation on their website.
http://www.bp-tec.com/They can also tune their unit in that you can choose how the recoil moves your rifle (straight in line with bore, etc.).
I have not tried one of these, but I would like to hear if anyone does. I know that theory and practrice are different, experience tells you how much. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />
jim
