For indoor use I'd much rather have something without the bark of a 8" or less barrelled rifle cartridge gun - the thought of firing my V51 indoors without a suppressor is something that makes me deaf just thinking about it. I have a .308 can but it adds weight and OAL to a point where it loses the pointability indoors I want in a HD gun.
I'm good with a pistol, but comparatively for accuracy and followup shots, I look like a drunken, half-blind conscript if I compare my pistol vs. carbine times and groups.
After 25m it gets even more pronounced.
The other point is there are times I'd like to bring something with a longer reach than a pistol but don't have room for a rifle, especially in ready to fire configuration. The K may be bigger than a pistol, but it's remarkably small for a carbine, and will fit in a laptop case or shoulder holster.
I also get to practice on a platform with the same manual of arms as my go-to carbine paying for 9mm vs .308, meaning far more practice time at a much cheaper cost.
It's also a hell of a lot more fun for me as a plinking gun than a .22 and about as cheap as can be had with a centerfire cartridge.
Of course, my taste in 9mm carbines runs to the extravagantly expensive. My old lady stole my Uzi, so I had to go one up and get a MP5-PDW clone made up:
These things are just plain fun to shoot, hitting 4" spinners at 50yrds is a breeze.
