I have the Knoxx on my 12 Ga. I attended a class shortly after installing it, and we shot nothing but 00 buck and slugs ALL afternoon. It was like shooting mild bird shot. Everyone else was starting to get a sore shoulder.
I am about to get a Remington, and will have a Knoxx collapsible on it.
It doesn't self absorb recoil in the air, it still needs the resistance of something whether it's your shoulder, or leg, arm etc.
If you think about it, if you could suspend a gun in air, a gun with a wooden stock or Knox will still fly back the same distance. There is no recoil unless it's against something. Otherwise it's just energy.
I have the Spec-op Knoxx on my Winchester Police Stainless, built on the model 1200 platform. Even after 7 shoulder surgeries, I have no problem shooting it. Maybe I should also mention this is a dedicated slug gun, which is a bit harder kicking than normal. I thought I would have to give up a shotty but Knoxx saved me and you'll find it is a quality built product.