The Blackhawk Spec-Ops (Knoxx) recoil reducing stock is outstanding. I put one on my 18" Mossberg 500 along with a Hogue over molded forfend. Shot it at the range with a friend's near identical shotgun, except he had some other brand of adjustable stock that didn't have the recoil reduction feature.
We were shooting slugs, 3" magnum buck and 00 buck. My friend shot a couple of 00 out of his, then he tried the same loads out of mine; and then refused to shoot his any more. So, we finished off several boxes of each out of mine.
It is rather odd looking, especially if you prefer a traditional looking stock. I normally do, but with this particular weapon, I wanted functionality over aesthetics. No regrets, I love it!