I'll be the decenter and devils advocate in this group. I'm old, I can take the abuse.
Being able to own a firearm that is in current use by the (a) military has a certain cachette... that can sometimes be hard to define, rationalize or justify.
I can't totally exclude myself from this fascination either, as I've been in the deep end of that pool, once possessing FN FALs, H&K G3s, SIG AMTs, a whole slew of US arms... and other sundry mil-spec weaponry.
I find that the M2 does everything I need a shotgun to do. Is it better or worse than an M4 at flinging quantities of buckshot down the lane? No... only different in the sense that they are designed for, and have different (intended) missions in life. Pick your mission, pick your gun.
I went with the M2 for a few reasons. I have (developed) an aversion to gas system weapons. Might be silly, but no more silly than any other illogical rationalization.
I liked the lightness and maneuverability of the M2... I have carpal tunnel and tendinitis, so this is an important feature to me.
On the other hand, I'm a fairly recoil-proof person, so that feature of the softer shooting M4 carries no weight.
The facade of objectivity is a tool of the master manipulator.