I wondered about that film. Thanks for the tip. I know they make tint sheets made specifically for helmets too, but haven't bought one yet.
The 3/4 helmet that I bought through dkrider -- I love it. They sell a tinted shield for it too. Their method of measuring worked fine for me... but.... it didn't work so well for my hubby. Ordered one for him but it was way too tight. Returned it for the next larger size and its still tight, but he's gonna keep it in hopes that it conforms to his head. They say people tend to buy too large anyway.
So I guess my point is, if you want to order one online, try to find some reviews about it and whether it fits true to size or not. JMO
As far as dual visor, my old helmet had a 3-snap shield, and I remember seeing dual visors that snap on that I thought would have worked on it, but unfortunately, I can't remember any details. (old age, yea)
Here's one I found on Amazon.... don't know a thing about it though.
http://www.amazon.com/Hawk-Black-Visor-Motorcycle-Helmet/dp/B002HLWQLQ