Legit.
I havent fired the .50 can yet, but the claims made to me by one of their industry partners about less bolt speed and blowby than baffled suppressors is on the mark. Translation: much less gas in the face and much less abuse on the rifle.
My only real hit on them is the size and weight of the cans, and that is only because it doesnt fit my requirements right now.
I would say they tend to be slightly, slightly louder but with a different sound. Its hard to describe.
The one I shot was on a full-auto SCAR that was a prototype conversion for 7.62x39. It was noticeably more comfortable to be around than my AK of the same barrel length and caliber which had a Surefire 762MINI. This was also shooting under a metal roof with no sound-dampening material which exacerbates noise even further. It was interesting enough to me that I'm now looking into the OSS stuff for some things I'm interested in.