If you carry a .22, .22 Magnum, .25, .380, and you ever need to use it, you will be soooooo sorry you didn't have a .45. The little guns are so easy to carry, and are better than no gun at all, but when you need to shoot at another human, it will not be enough. What you will need at that time is the most stomping power that you can carry. A little gun might turn someone away from their hostile intentions, but it probably won't.
I saw the effect of different calibers during my long career as a cop. Sometimes, the .380's will kill, but never have I known an instance when that caliber or a lesser caliber stopped a person immediately. A .380 is top of the mouse guns, but it ain't at all reliable in saving lives. Even head shots are usually not lethal. A puny round stops on contact with the skull, and no few times have I known .380s and .22s to strike the forehead and follow the rim of the skull under the scalp and exit at the back.
That said, they are not completely useless, and some folks upon being shot, fall down just because they know they've been shot. I carry a NAA .22 Magnum in my pocket, and a .45 in my belt.
I'm just saying, if you carry, carry enough. Your chances of surviving a shooting encounter with just a mouse gun, is minimal.