i wear a fullface most of the time especially on unknown trails. After a hard crash i decided to not care what others think about it and just wear one.
Absolutely right about try before you buy. I bought a MET helmet before that was the right circumference for my head, but was actually tight up against the front and back of my head, I've personally found specialized/s-works and Oakley fit perfectly: I can't fit one finger between my head and the helmet when wearing it, but without being tight. But then the MET helmet would be perfect for someone else.
IMO more brands should start making smaller, light, propper ventilated full-face helmets, for riders who dont ride DH but would like to have chin protection.
Majority of my riding is trail and I have previously only had half shells. After a recent crash ended in heavy concussion and 4 broken ribs I have now got a Bell Super Air that can convert between half shell and full face. Not many manufacturers offer these convertible models but I think they should.