I was running paintball at my work and someone showed up with one of these on. Seemed like an amazing idea that all of us should be saying "duh, why didn't I think of that" I can see it being handy for our low light games where mesh folks will sometimes complain. https://www.youtube.com/watch?v=KhPUXgtICgM
especially nice because you can use an all types and only need one for multiple pairs of goggles. I think that Tom may have some for sale.
I would be interested to see someone try and make them on their own locally. Just have to make sure the fabric is thick enough that the magnet doesn't scratch the lense.