This is the kind of fine tuning that could be done after the basics are right.
It doesn't matter how helmets behave mechanically as long as combat is just about high ground and cheesing in various ways. Nothing does.
Mechanically, I'd like helmets to have some kind of tradeoff. So that NOT wearing a helmet could also be a good option. It's silly if every mage or rogue in leather wear a full metal helmet for protection just because they can.
I don't like the "hide helmet" feature either. If someone wears a helmet it needs to show. Maybe it's significant mechanically or to reveal a faction or something. You might as well have a "hide armor" feature to make your full plate look like a chainmail bikini. If not wearing a helmet had a mechanical reason, you would have less reason to hide them.
