I'm another one who likes invisible helmets: I just like to see my characters. I like my armour to look reasonably realistic (or at least practical, even if not entirely authentic) but I'm not a fan of helmets simply because that's my aesthetic preference. Obviously IRL I'd rather not be clonked on the head with a heavy object, but in a world where magic prevails, I see no problem with invisibility.
Of course, the issue with that idea is that if the helmet can enchanted to be invisible, the chainmail bikini can also be excused as a selective invisibility enchantment...
(Disclaimer: I think the chainmail bikini stuff is dumb but I don't really care about whether or not helmet display can be turned on or off.)
