To quote noted fighting shotgun instructor Louis Awerbuck, "No magazine is ever big enough." If the situation is bad enough, you will run out of the ammo in the gun- unless you practice loading the gun on the fly, and have extra ammo readily available on your person or on the gun. Often called 'shoot one, load one,' it's a vital skill if you use a tubular magazine shotgun and ever get into a protracted gunfight with it.
The good news is, very few armed citizens ever get into protracted gunfights with anything at all, much less shotguns. The bad news is, if it happens to you, then it's not too likely that one or two more rounds in the original magazine load will make much difference either way.
Learn to run the gun, if you're serious about your question. Software trumps hardware...
JMHO, YMMV, FWIW...
lpl