I don't worry so much about rimfire ignition in a revolver. I'd as soon have the Black Widow as a .32 auto, personally, though reloading is a pain. But, you should pray with either weapon you don't get into a protracted gun battle. Actually, you should pray with anything you don't get into a gun battle, but the .22 doesn't give me confidence in stopping the fight anytime too soon, put it that way, at least without a head shot. I can say the same about a .32. My self defense calibers start at .380 and I prefer a .38 or more. More caliber the merrier. If I can a given day, I'll carry a .357 magnum or .45 IWB, but I can pocket my 9x19 and that's what I usually carry. I see no reason to choose a .22 or a .32 when I can carry a .380 just as easily or even my 9x19 about as easily. I do have to buy my pants with the 9mm in consideration, but it can be done.
One problem with .22 mag in such a small gun is the fact that the slower powders loaded in these rounds are really intended for rifles. A 2" barrel really neuters the cartridge and it's more flash/bang than velocity. There is some added performance over .22LR, but not enough to make me feel confident in it.
All that said, I do carry and very much like my little NAA mini .22 with holster grip. It's so small, it goes along ALSO, not alone. It is back up and varmint dispatcher many times. Even in .22LR, the muzzle blast is loud. The magnum sounds like a .38+P or maybe a little more.
Now I've been wanting a mini master for a long time, with a mag cylinder. I might get that one next because I can't think of anything else I'd want at this time. I think it'd be a fun novelty/plinker. It might even be amazingly accurate with the added sight radius. My little mini is pretty amazing. Well, I think 6 or 7 inch groups at 25 yards off sand bags is pretty amazing with a sub 2" sight radius, LOL! It's good 'nuf to be useful at shorter ranges, 10-20 yards, for some pretty small targets, like 5 yards on a snake's head. Pulled that one off a half dozen times when the NAA was all I had that was appropriate for the job (would have gotten mud all over me with my .308, for instance).
Oh, I load my NAA with Fed Lightening, but about once a month, every two weeks if I think about it, I dump it and reload with fresh. .22LR is heal crimped externally lubricated and moisture can get into it easier than a mag round. In hot summer when it rides in a sweaty pocket, sometimes I'll change ammo once a week. I mean at less than ten bucks for 550 rounds, no since in taking chances with old ammo. For some reason, my NAA LOVES this stuff, shoots to POA and is quite accurate.