The chief disadvantage to any pistol-gripped long gun is weapons retention. (read Mas Ayoob on this). If you never seen this (in military combatives training e.g.), when someone grabs the front end of your weapon and twists up and back, your only options may be to let go with your dominant hand (losing the weapon, and maybe getting shot with it) or having the saddle joint of your thumb broken (before letting go, losing your weapon, and getting shot with it). Given that a tactical shotgun is MEANT to be used for close quarters confrontations, I personally would NOT want a pistol grip on mine.