German is Fledermaus if I remember correctly, so Flittermouse seems to be Germanic in origin, as is the Swedish word, fladdermus. Etymology is interesting, but I know next to nothing about it. Guessing is fun, though. If I'm wrong here, I love to be educated.
I get why bat is preferred as the Germanic versions are more than a little clunky and not nearly as cool or scary sounding. Here comes the amazing Flittermouseman! Villains beware!
Raspy voice "I am Flittermouseman".
You are correct. If I gave the impression that it is a safe endeavour, I am sorry. It is safe IF done correctly, but it can get explodey if you fuck up bad enough.
Do your research, keep it small scale and don't sell.