I'm calling bullshit. I don't think you can silence any weapon to that extent much less a shotgun.
Checked their website and they actually posted all the relevant specs, looks like bullshit it be in that YouTube video.
dB AT EAR:
12" - 132.0
10" - 134.1
8" - 137.0
6" - 140.6
Those are decibel levels that will require the use of hearing protection. Here is some decibel level research:
12 Guage Shotgun Blast is 165db, every 10 decibels is twice as loud so this is significant sound level reduction but it's anything but movie silencer quiet which honestly does not exist outside of movies.
Environmental Noise
Weakest sound heard0dB
Whisper Quiet Library at 6'30dB
Normal conversation at 3'60-65dB
Telephone dial tone80dB
City Traffic (inside car)85dB
Train whistle at 500', Truck Traffic90dB
Jackhammer at 50'95dB
Subway train at 200'95dB
Level at which sustained exposure may result in hearing loss90 - 95dB
Hand Drill98dB
Power mower at 3'107dB
Snowmobile, Motorcycle100dB
Power saw at 3'110dB
Sandblasting, Loud Rock Concert115dB
Pain begins125dB
Pneumatic riveter at 4'125dB
Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection 140dB
Jet engine at 100'140dB
12 Gauge Shotgun Blast165dB
Death of hearing tissue180dB
Loudest sound possible194dB