I tried out the Smith Turbo fan series which are OTG and they worked extremely well. Basically a battery powered fan built inside the goggle that keeps your glasses from fogging up. You don't even realize it's running.
I wish I'd have bought them, but already had a pair of Smith Prophecy OTG that I purchased a month prior. Couldn't pull the trigger on 2 sets of goggles that close together.
I believe this is what I demo'd -