What's the advantage on a Gasbuster on piston rifle? It's selling point is that it claims to stop gas from getting into the shooter's face (is this a massive problem for ARs - never heard of it), but there isn't any gas going into the receiver on the HK (or any other piston AR). Looks like just a big handle that doesn't really offer any improvement over the HK handle.
Yes, there is a fair amount of hot gasses that get sent through the receiver and get on the face of or in the eyes of the shooter when shooting suppressed. Take a look at a person who has been shooting a DI AR suppressed for an hour and you'll see black smudge all over their face and shooting glasses. Not cool.
BUT, the cause of this isn't from the gasses coming back though the gas tube, otherwise this would be an issue with all ARs, not just ones running suppressed. The issue is that when shooting suppressed, the suppressor catches a fair amount of expanding propellant gasses, and then after the bullet has exited, those gasses continue to expand and go both directions, out the front of the supressor and right back through the bore into the action as the rifle is cycling.
This happens on ALL semi-automatic rifles when running suppressed, piston guns included. Of course it is worse on AR series rifles as it has the rear mounted charging handle which provides more escape routes for the gasses, but it still happens on all rifles. If you have a change to observe two piston rifles of the exact same type, one running suppressed and one running non-suppressed for the exact same number of rounds, you'll notice that the suppressed gun is far, far dirtier then the unsuppressed. Even dirtier then an AR15 (unsuppressed). Ar15's suppressed look like the devils ******* after shooting a few hundred rounds suppressed.
The Gas-Buster provides side vents to direct the gasses away from the face and a larger handle to "catch" the gasses that don't re-direct. It doesn't work 100%, but then again, nothing like this does. There wil still be a little bit that escapes, but it is far more pleasant to shoot a suppressed rifle with a Gas-Buster then it is without.
I speak from personal experience.