I don't think the first reply understood your question since he talked about LRN which you did not mention. To answer your question, I agree that it is not a good choice for a self-defense round. While it will transfer all energy upon impact, similar to a glaser safety slug, it will not penetrate adequately. LRN (lead round nose) would be a better self-defense round IMHO than a frangible load.
There are companies (DRT for example) that market frangible loads as self-defense ammo, but personally I am not sold. I believe about anything, LRN, FMJ, JHP, SJSP, LSWCHP would all be better defense rounds than frangible. Just my .02