I dunno. One of the benefits is the huge magazine capacity, but I live in California, so...
It also seems, at least on the surface, that it would be a good choice for a small, light, concealable gun, but those don't seem to exist. Perhaps in a short barrel, the little bullet loses too much speed, which would make it nearly worthless.
Beyond that, it seems like a good cartridge for pests, but I don't think I'd go after big game with it, and that's kind of my "floor" for a defensive cartridge: If I wouldn't shoot a calm, unalarmed 200 pound animal with it, why would I trust it to work on an enraged 200 pound man who wants me dead?
So, yay capacity, yay decreased recoil. Boo full-sized guns, and boo (maybe) a little bullet that doesn't do enough damage in flesh.
So I guess from where I sit, it's a pretty specialized cartridge/gun, which sits well in an OWB duty holster worn by a professional who needs to worry about suspects with body armor. For the rest of us, I'm not sure I see the niche.