Specialized tool
The Serbu shorty or any short pistol gripped shotgun is a tool for special applications. I used to carry a 870 that was cut off at the pistol grip and mag tube under a jacket when I was doing high risk transport details for Uncle S.
This had the blessings of the U.S. Gov't. We carried them with WW #4 buck.
Rigged them with a bungee cord similar to a "merc harness" for under arm carry. I have carried one under a windbreaker along with my pistol and mags and never been made for being armed. They are unpleasant to shoot, but at 7yds to contact range they are awesome.
Not something for the meek or timid, they have a tremendous muzzle blast, huge muzzle flash and lots of felt recoil. Specialized tool for specialized applications. Bigger hammer for bigger nails.