Following the Munich Olympics tragedy the Israeli Mossad elevated the .22 Beretta into "cult status," but their use of that weapon had nothing to do with self defense.
The .22 in any configuration can be effective for self-defense, but the key is "placement, placement, placement" -- and in the sudden stress of self-defense situations that can be problematical.
Still and all, if a .22 were all that I had available, I would be damned glad to have it.