is giving simultanious displays harmful to my chess?


Yes, your head may asplode.
No, I don't think blindfold can fix an asplosion.

Also, playing bullet chess doesn’t harm you unless that’s all you play. A few games of bullet can sharpen your ability to spot tactics more quickly, but obviously if it’s all you do, your other games may suffer.
The key is to spend most of your time with what you want to be best at, but doing a little bit of anything may be a fun for a little change to help keep the game fresh for you.