.22 mag for self defense:
Sure it will work for self defense if that is what you choose to use for that purpose. Especially if loaded with the newer Federal 50 grain hollow points. Tested them and they are awesome for a small .22 caliber handgun. I have a .22 mag revolver myself (S&W model 51 w/4" barrel) and it is very accurate and reliable with nice trigger pull as well.
Main thing is, if you have confidence in it and practice shooting it on a regular basis it will do the job. Having a .38 or .357 that you don't want to shoot or practice with will do you not much good when things go south. Personally, I like a .45acp but that is another story. However, I would still feel okay with a .22 magnum if I was familiar with it and practiced shooting it regularly. But that goes for any handgun for that matter. Good luck