I have one on a Mossberg 500 12ga 18.5" smoothbore. It is the Mossberg one as described above, and gives me 5-6" groups at 100yds, and usually 2" or so at 50yds when I do my part. Now those groups are with regular practice. I wanted to see what would happen without it, and after 6 months of not shooting this gun, I went to 4-5" at 50 and 11-12" at 100 yds, so practice is definitely very important with this gun. I shoot it at least once every couple months to maintain accuracy with it. This started life as my defensive shotgun, and still serves that purpose, but it is seeing more and more hunting use as the years go by. I say pick one you like, and go see what your shotgun is really capable of with some practice and slugs it likes.