The Benelli is a recoil operated shotgun and is very reliable, but is the hardest recoiling semi-auto. The 11-87 is a fine shotgun, and is gas operated, which significantly reduces recoil. In fact, the 11-87 is the lightest recoiling Tactical shotgun.
The 11-87 or 1100 must be kept relatively clean to insure reliability, but that shouldn't be a problem. I keep my 870 clean. If the Benelli handles low recoil ammo, like Federal Tactical or Winchester Ranger, then it would be a fine choice. If you have to use full power Buckshot to get cycle reliability in the Benelli, also, then I'd prefer the lighter recoiling 11-87. To be honest, I'm not sure which one to buy if I decide to add a semi-auto.
Right now I'm an 870 man, and I wish my new Scattergun Tech Combat shotgun from Wilson would arrive with it's SureFire Tactical fore end and other features.
To answer your question, the pistol grip is more useful for Police Tactical Units where one might need to hang on to the shotgun with one hand while using the other to manage essential gear, open dooors, and so forth. An officer could shoot one handed in an emergency.
Folding stocks are useful for one purpose only, which is storing when space is limited. The folding stock is MUCH inferior when the shooting starts. Finally, stay away from pistol grip shotguns. Firing will need to be done from the hip and they're not easy to control. Pistol grip stocks are the worst for weapon retention. My vote: Standard stock.
