Some other real world considerations for the AA-12.
The magazine is noisy, the rounds seat well enough but it still rattles - so much for stealth
Reloading requires that the magazine slot into the strut in front of the trigger - try doing that at night, in the cold, with slippery hands - there's a reason most of the YouTube clips don't show them placing a fresh mag on the shotgun, because then you'd see the primary failing of the AA-12.
The magazine HAS to seat on that strut, otherwise it'll move around too much and weaken the mag catch because it's too heavy for the magazine well
The USAS-12 is every bit as good as the AA-12 with a much lower cost and better availability but it still hasn't been taken into service by any military/police agency in significant numbers.
So if the cops and the soldiers didn't buy the USAS-12, they wouldn't bother with the AA-12 especially given the weakness in the magazine setup... unless of course a slick ad campaign can convince the politicians that the AA-12 is the "World's deadliest shotgun!" and will rewrite the laws of urban combat
