I wouldn't wear on 'old' helmet or one without a 'DOT' sticker that was for real, manufactured into the product. As far as 'lids', I like to wear a Police type half helmet. It's just between cool beany and modular. I have a Fulmer modular flip-face helmet and feel safe with it, pluss the benefit of having a flipped up open face. Beany's will protect, but only marginally, it's just by design. A full face is about as good as it gets, thus the modular. My feelings on not wearing a helmet.....? It's asking for trouble if an event should happen. I also think even states where no helmets are required that the Law (Cops riding by) would think you likely a safer rided and their impression while seeing you would be 'a look then dissmissed as a target' for citations. I just dont feel any kind of safe without a helmet.
Arguments can be made both ways on the helmet laws, but beyond that, a half helmet or none at all has alot of 'wind noise' to contend with, and it is fatigueing to hear the constant wind roar. I'v lost aquaintances with both helmets and no helmets, but I think if your skiding along from 50 or 60 you'll find Mother Earth pretty unforgiving