I have played with this in 20 degree and 90 degree weather. No fog. The two times I installed it into my mask took about 20-30 minutes each. My fingers hurt like crazy.
Could be cheaper, was 20$. Scratches relatively easy. I have a JT Alpha 2000 mask, perhaps it is easier to install in other masks? I hope so. This lens made that average mask into a great mask for me!