Has anyone used one or have one? I haven't shot anything with a suppressor but
this looks like it may be worth looking into.

I looked at them carefully when the Silencer Shop was closing them out and called about them. The word from Silencer Shop was that the design was targeted very specifically at situations where low back pressure was essential. They basically said that if you don't already know that you need one, then you should probably go a different direction. For once, I took the professional advice and went the different direction with a Griffin Precision Hunter 338.

I have an adjustable gas block on one upper(6.5) and not the other (223)and it seems it doesn't matter but I saw where you should have to only replace the SRM module (front part) after a ton of rounds. Of course the video's I watched made the suppressor suppressor super quiet.

As I recall, the db suppression was actually very ordinary compared to a number of other units on the market. The ability to replace the SRM module certainly looked like a good thing, but I don't think the market really embraced the unit. I was very seriously interested and watched every video available at the time and read every article that I could. I think the OSS was really targeted at full-auto usage where all of its virtues would really come into play. Without full auto, I don't really see the unit as being exceptional.

Not sure what these are more popular, I assume price. I shot a few rounds threw a demo and it reduced noise and recoil like all of them. The best thing about it for CQB is that the length isn't nearly as long as a normal suppressor. It's old technology for the most part, based off an original suppressor design