I used them for 2 seasons. At first they were great, allowed air flow but kept ice from building up.
But about halfway through last season they got clogged up and no longer allowed air to flow through them despite looking clean (mine were yellow). I ended up ditching them because we didn't have much for powder days last year and there were making my bike overheat. The velcro is so strong that it pulls the sticky part off of the bike before the velcro separates, so removing them frequently didn't work very good.
I'll be back to sliding a solid piece of plastic behind the plastic radiator louvers on powder days to keep snow off the radiators.