The real market for such guns is in places with firearms restrictions. Many parts of europe including the UK have exemptions or at least more lenient laws for what are called garden guns. Sometimes some countries may exempt the .410 into that group of low power shotguns. The classic cartridge is a 9mm rimfire firing about a 1/4 oz of number 6 or 8 shot at 600 fps. In a smooth bore good to go from one end of a small garden to maybe the end of it. In the UK those were IIRC called rook guns. Typical such ammunition.
I am sort of playing with the idea of trying out a 9x19 case with a .38 spl speer shot capsule to fire in a 9mm carbine. I might ream the rifling out to make it smooth bore. At this point many other projects so it is just day dreaming at this point.