I see you point perfectly guys. However, it's coming from the range/competition/hunting perspective exclusively. In the survival perspective the options above do have their serious place. You can stock on a ton of ammo, but you stockpile could be destroyed, stolen, unreachable, as well as your beloved zeroid in carbine. Then just dig out your hidden doomsday cash with a cheap 12 ga and these inserts. It's hard to have a lot of ammo for 12 ga in such a cash, neither carrying a lot of it out of the woods at once, but who cares - as with the inserts any scavenged or traded ammo will do just fine for the close quarters shelter defense and some hunting. Looking at the inserts length I can tell that at least they are providing noticeably longer barrel than your typical handgun, so it's probably should not shoot any worse (except that for a better gases dynamics it might be beneficial to saw off the shotgun's barrel some).