So, my understanding is that the reason the evokers look like guns is to elevate the user's stress levels and essentially "scare" the persona out of them when they pull the trigger. And obviously, they don't really fire bullets or the game would be over pretty quickly.
However, do they perform any mechanical function at all? Do they fire some sort of psychic energy, or make a sound, or anything? Or are they essentially just a metal frame with a spring-loaded trigger?
Presumably these questions also apply to Koromaru's evoker collar, since it doesn't seem to hurt him.
Eurogamer has a fair share of opinion and personal pieces on their public feed, and they have even more of it in their subscription tier (I cannot comment on the quality of those as I'm not a subscriber, I just see that they post them).