My HJC modular helmet had a slide down sun visor. I always wear polarized prescription sunglasses in the day time and used the visor a few times, but never found it very useful.
For the limited amount of time when I'm riding right into a sun that is low in the sky, I usually tilt my head forward so the top of my helmet opening acts as a sun visor.
A few times riding right into a sunset Ive had to hold my hand out to block it.
Makes me wonder, I have never seen anything like a sun visor for a MC windshield, but I'm sure someone must have done it.