I purchased a Mossberg 591a1 not too long ago. It is this model HERE
My main reasoning behind this weapon was for home defense purposes. I took the gun to my local range to get some practice in with it, and to have a little fun. I did a combination of slugs and 00 buck.
I noticed that the recoil of the slugs was significantly more 'sharp' than that of the buckshot. After only 5 or 6 slugs, I was tender enough to not want to fire anymore.
So I did a little research, and found this at Cabelas.
The installation was simple enough. Just unscrew the factory butt stock, and attach the Knoxx via the same bolt.
Went back to the range, and instantly noticed a HUGE difference. There was much less felt recoil, and my shoulder held out the entire time. Now, they advertise as "95% less felt recoil". I don't know if I'd take that to the bank, but it certainly reduces the felt recoil and makes shooting a lot more enjoyable and longer lasting.
It is an adjustable stock, so I'm able to shorten it for fitting around tight spaces, or lengthen for trips at the range.
My only quarrel with the Knoxx is during the dis-assembly process. In order to take down the trigger assembly, the Knoxx must be removed first. Not a major pain, but an inconvenience.
All in all, this stock is a wonderful addition to my HD shotty, and I highly recommend everyone giving it a try with your guns as well.