The M26 is a breaching tool and not designed as an anti-personnel weapon. It was chosen by the US military over the KAC Masterkey and Remington MCS Accessory Weapon, both of which use the Remington Model 870 shotgun as a base. The M26 distributes its weight further back compared with the 870 and so it feels lighter.
http://www.thefirearmblog.com/blog/2010/02/16/the-c-more-m26-may-be-available-to-civilians/
I wouldn’t buy an M26 anyway.
First, the US military mostly uses shotguns only as breachers or anti-boarding weapons. The remaining users are MPs/guards, that sort of thing. Even so, the Marines have moved away from manually actuated shotguns - the Benelli M4 is currently issued by the US Marines as the M1014 shotgun. Manually operated shotguns are prone to operator error under stress, so people are moving to auto loaders. The M1014 is replacing Mossberg 590s and Remington 870s in most service applications now. The Marines are also reportedly looking into converting their 1014s to box magazine fed.