The problem with snowmachine visors is the build up of moisture from sweat. Even the very best helmet with the very best breath deflector will eventually cloud up with sweat from your cheeks and moisture from your eyes.
I had a heated visor that would prevent fogging but eventually you had to wipe the moisture away to see clear again. The wires connecting the visor to the sled proved to be a pain in azz.
I ended up going with a helmet that had a really good breath deflector and tight fitting goggles that wouldn't let air seep past and cause frostbite on my cheeks. I used a Scott goggle anti-fog cloth to wipe the moisture off and treat the goggles. It was THE best set up I found.
FWIW, liquid Rain X will screw up the coatings on plastic ski goggle lenses.
