sorry for the post resurrection but hopefully this will help others..
i just bought one, ROTEX - X, and fired a few shots today and was extremely happy!! its MUCH quieter than my other 2, SAI CQS-50, ASE UTRA DUAL 5.56.. both QD systems
i was hesitant at first also due to the advertised -30db reduction, but i can attest to that, i fired off a single 855 into the ground off to my side and was shocked, i guess it hitting so close after leaving the muzzle it didnt break the sound barrier, but it sounded like a fart!! so i shot a few 855's at 50m and as expected, fart, then normal ground impact thud and supersonic crack, so i then tested the hunting rds i have, federal gold medal berger 223, 73gr HPBT, and it was even quieter out of the barrel, but again..thug and crack so im sold and can confidently recommend this suppressor