At first I thought you might be talking about the helical suppressors made by OSS. They encompass more of the barrel than most modern suppressors. They have fins and channels that direct airflow in a helical pattern instead of using traditional baffles to trap gasses. No experience with them, but supposedly they are efficient. The open ended front supposedly minimizes the "gas in the face" effect when used on an AR. The reflex suppressors you linked are old technology from Eastern Bloc suppressors. The large volume around the barrel is basically acting as an enlarged blast chamber (the first void in a suppressor is called the blast chamber - it is typically larger than the subsequent chambers and is often reinforced to withstand higher heat and pressure, as is the first baffle in the stack, called the blast baffle). A large blast chamber is good, but the reflex suppressor is trying to trade off an excessively large blast chamber for an extremely short baffle stack. A larger blast chamber isn't enough to compensate for an inadequate baffle stack. Modern suppressors are far more efficient.