The Benelli M1014 is the first gas operated shotgun they made. Not all Benelli's are inertia.Not to hijack the OP's thread, but when it comes to auto's the biggest decision other than price, is gas or inertia in my opinion.
Beretta, Browning = Gas
Benelli, Franchi, Stoeger = Inertia
Benelli's are a sweet rig no doubt. You can beat them to death and they keep going. Franchi and Stoeger are very similar to the M2. Some parts interchange. One major difference is the the inertia spring is on the mag tube vs in the stock on the Benelli. Others can chime in on additional info. A Stoeger is a great budget friendly auto with some high end features.
I have a CZ1012 that's inertia. It's very close to a Benelli design with spring in the stock but you cannot add a mag tube extension and the safety is forward the trigger. That said, I love mine and it's great in the price department.
Hit me up if you want to run some through the paces.