Auto darkening face shields

Has anyone had any experience with the film you put on the inside of the face shield that turns dark in sunlight and lightens when the light decreases?

I was wondering about the optics, clarity, etc.

 

My welding helmet does that but I don't think it is DOT approved.

 

Interesting concept but I would be concerned about going into a dark area like a tunnel or similar that it would lighten fast enough to be able to see OK.

 

Thanks for the info, do you have a link to them?

 

Thanks for the link, interesting product for sure.