Wow, I'm confused. I thought the OP's question was about a shotgun with a pistol grip sans a shoulder stock. The pistol grip only shotguns take a lot of practice and they are hard on the wrist, as already noted here. The shoulder stock shotguns with a pistol grip are a different animal.
I have a pistol grip on my mossberg 500. The pistol grip came with it when I bought it new. Its a hip gun with the grip on it cuz the recoil will smack your face if ya use the sights. Its great for home defense if ya can handle the recoil to the hand