Are Mini Shotgun Shells Viable for Self-Defense?

Within just the last few years, 1 3/4" mini shotgun shells have gone from quirky novelty status to an ammo option that firearm and shotshell makers seem to be taking seriously. Mini shells offer reduced recoil and increased ammo capacity -- ideal features for a lot of shotgun users. But are these pint-sized 12 gauge loads just as effective as the standard 2 3/4" shells? Or is there some kind of tradeoff? We measured and tested four different mini-shells to find out their muzzle velocity, how they pattern at home defense distances, and their performance in ballistic gelatin.