I have just aquired a SGA stock for my new to me 870 Wingmaster with a 12.5" barrel. So far i only have one outing with it, where I fired a variety of 3" slugs, 2.75" slugs, and 2.75" #2 Mini Magnums.
I'm very impressed with it. The ergonomics in the grip are a great improvement to the conventional stock synthetic butt stocks I am used too. I have it set up for the shortest LOP possible and didn't experience any thumb collisions to the nose that some have claimed with other brands of short LOP stocks.
They are a bit heavier than a normal plastic stock, but the extra weight in the rear actually helped balance the gun when practicing tactical reloads while staying in the firing position and keeping the muzzle on target.
Felt recoil was tolerable, but you still felt the punch of a 3" slug.
I didn't opt for the MOE forend as it protrudes further than the mag tube cap, and on a short barrel model like mine, it left me no room for a forward sling plate. Also mine came with a Houge rubber forend which I find nice and sticky.
It is an odd looking stock, but the looks do grow on you. A buddy of mine promptly ordered one for himself after seeing mine and listing to my review.
Here's a pic as it sits so far.... next I plan to paint it FDE to match the FDE stock.