I do not know, mainly because I wear the helmet anyway.
Got a sharply pointed object lesson one day about both helmets and enclosed-chain drive mopeds.
Was making a U-turn in the median, which isn't exactly picture-perfect traffic behavior, but beats getting creamed by a truck...and the damn chain master link popped.
Normally that'd just mean the chain gets flung off, right ?
Not in an enclosed-chain drive it don't....the chain wrapped around the rear sprocket and jammed, and it was like taking off after trying a 50 foot rope from the back of your 'ped to a fence....and running out of rope - Pwiiiinnggg.
Over the handlebars my puny tail went, headfirst into a nice sized rock.
Sat up, shook my head and pulled off my Shoei full-face helmet, and lo and behold, a big nasty chip in IT, instead of my head.....I've worn a helmet ever since, but preference is 3/4 open face with goggles, face shields fog and distort too easy.
I also rip the box off any "enclosed-chain" 'ped the minute I get it.
I figure it's your choice, more so than a matter of law, but I choose to wear one, I also choose to wear motorcross armor under my jacket, but no one seems to keen on making that a matter of law, do they ?
Of course, I might be a little biased, since using the aforementioned equipment, is the reason I happen to still be here, even though I do agree that some of the heavier helmets are as much a danger as they are a help.
And fer crying out loud, why can they not simply drill a small hole over each earpiece and cover it with mesh or something so you can HEAR the truck about to back up over you when you're looking in the other direction, eh ?
Still, I figure it should be up to you.