I have a kel-tek plr16 .223 pistol. Even outdoors, it is so loud that you really want ear plugs and ear muffs. I imagine that unmuffled indoors it would result in permanent hearing loss.
It runs great, is light and compact, surprisingly accurate, uses ar15 magazines, and is a total blast. It is a real crowd pleaser. I like the idea of normal capacity 30 round magazines for emergency defense, but I personally think that handgun calibers are a better answer for most home defense needs.
But, on the other hand, I am always for any reason to add to the personal arsenal. Sometimes you just NEED it.