It makes no difference wether the two wheels of a trike are at the front or the back if they are far enough apart it can be registered as a trike. If so the rider doesn't have to wear a crash helmet, I would!. there are other requirements like a foot brake and a parking brake, etc. Therefore they can be driven on a car licence if your test was taken before 2013, don't quote me on that but I think it's correct. I've never seen anybody riding one without a helmet and I wouldn't do it. I once tried it when it was still legal to do so but didin't like it at all.
The wind in your hair may be nice but over my bald scalp not so much.
