It's almost a contact weapon and requires eye socket hits. I can at least shoot mine since I put a folding holster/grip on it. Without the holster grip, I can't grip the thing. It will work up close with proper hits on the head, I'm quite sure. I often pocket mine in my weak side pocket in addition to my 9x19 or .38 special, but I never carry the thing as a primary. It's pretty accurate if you have the time and the light to align those tiny sights, but it's not much of a point shooter and you can't count on having that much time.
I figure in a fire fight, if I were behind a barricade, hard cover, it DOES make a lot of noise and maybe could keep a guy's head down while I clear a jam or something, not that I've ever had a jam, but I'm just sayin'. But, it's beats a knife up close since I don't really like knifes.
Mine's a .22LR. Best I can give you on effectiveness is the feral dog I head shot with it at about 25 yards, DOA. Yeah, a little luck in that shot. The thing groups about 6" at that range from a bench being REAL deliberate.
It stiffened up and just fell over. I have that thing with me a lot and didn't have anything else when I caught this mangy critter chasing chickens. I didn't wanna get too close to him, mange city and drooling. Hit him right in the head near the left eye. Yeah, a CNS hit seems to work, at least on a 60 lb dog.