As a familiar? Do you mean, like keeping a bat as a pet?
I just recommend against that altogether.
As for personality, all of them I've seen pretty much acted like vicious flying rodents. I've captured exactly one (relocation from an urban area where it was unwelcome to a pasture) and it mostly hung out, shit, and got hissy if I looked too closely at it. Personally I was glad to see it go, I was happy to help it out but I don't think it wanted to be friends.
"The devil I'll bring you," answered Hagen. "I have enough to carry with my shield and breastplate; my helm is bright, the sword is in my hand, therefore I bring you naught."