One could argue that if one has something like a Rem 870 with both a shot & slug barrel, a good all-around rifle and a few pistols (maybe some that can be modified for different calibers) you have it all covered anyway.
As I watched the range clips this guy had, I saw the short barrel lengths affect accuracy, in a SHTF scenario that is not a small issue. Not being a gunsmith I cannot speculate how long the barrels would need to be to improve accuracy (especially the rifle calibers), but something like this may be better suited for the low budget crowd who may already have a double barrel in their possession looking to fill out their bug-out bag and be able to shoot whatever calibers they happen to come across or have on hand.