I bought one of these little blasters a few months ago, after years of debating whether I wanted what I thought was a novelty gun. As soon as I got my hands on it, I was very impressed with the craftsmanship of the revolver. Make no mistake, despite it's diminutive size, these are serious, quality firearms.
About the time I bought mine, ammo makers began cranking out .22 magnum self defense ammo, making them in my opinion, viable self defense tools. I bought and tested (unscientifically) three brands; Federal TNT, Speer Gold Dot and Hornady Critical Defense. In my back-yard water jug tests, all three produced impressive results for penetration and expansion. The one which really grabbed my attention was the Critical Defense. The bullet impact was most impressive, with penetration over 15 inches. Bullet expansion was out to about 9mm, which IMO makes the lowly NAA Mini Revolver .22 mag a serious back-up, or as my neighbor likes to call them a "taking the trash out gun."