The main advantage of the Benelli M1 is its interchangeable chokes and the availability of sporting length barrels. However, this is only important if you intend to use your shotgun for hunting and/or competition, in addition to self-defense.
Other than that, I'd say that the Beretta 1201 is a fine choice. It is for all intents and purposes a Benelli M1 with Beretta markings. With the main exceptions of the barrels, magazine tubes, and carrier stop/cartridge drop levers, the majority of parts should be interchangeable. In fact, Benelli supplies some of the parts to Beretta. (Beretta has had a financial interest in Benelli for some time, and finally bought the company a few years back.)