Saw a picture of it and wondered if that grip operated the slide? Appears that it does.
Obviously made for short range defense against closely packed adversaries since you can't use sights at all...my guess it is aimed at the Zombie Defense League. I guess it works if you have a pistol grip only shotgun, since you've pretty much given up using the sights and committed to hip shooting.
Reversing the grip and having it at the bottom would be more practical on a standard stock weapon, and more inconvenient, allowing you to retain the weapon under rough action and give a more secure grip of the forearm and still allow sighted shots.