I had a buddy who was a police officer and installed one of those on his Mossberg 500 (police issued) shotgun. He practiced with it until he got very good on static targets. He then upped his game by having his dad stand behind a small hill (for cover) and throw clay birds for him until he could break them regularly. He upped his game even further by having his dad (still behind the hill) throw the clay birds directly at him. By the time he could break those clay birds, he had wrecked his hands and wrists and could no longer shoot the pistol gripped Mossberg (he had used #4 Buckshot through all of his practice sessions). I think a pistol gripped shotgun gets high marks for portability, "coolness", and compactness, but I wouldn't want to shoot one on any kind of regular basis.
Good luck,
Dave