I have the speedfeed PG/Buttstock on one of my 870's and I like it. This particular 870 is my "artillary piece" and has a 6rd sidesaddle, extended 6rd tube (loaded with 4) and hogue forend.
I like the SF stock. I keep 4 rds of buckshot in it and, combined with the 4 in the tube and the six slugs in the sidesaddle, I feel pretty prepared! The gun is heavy and thus is my HD "barricade gun" rather than my "Search/House-clearing gun" (870 Wingmaster with 4rd sidesaddle, 18.5" barrel, and std. wood stock) or my "car-gun" (Mossy 500A with 2pt bungee sling and butt-pouch with 5 slugs and a survival kit in the zipper pouch.
I'm toying with purchasing another 870 and adding a Knoxx Specops stock and surefire forend (to match our department guns), then switching the SF stock to a folding stock and making it my car-gun, using the 500A as my house/search gun, and the wingmaster as a backup/fun gun.