Really depends on the environment. In drier climates it's awesome. People report that it's less effective in humid climates. I've used in both Vegas and Cozumel, and noted that it worked better on the bike in Coz with a good wind passing over it than on the run. Wore it at Canada last year, dry and 95 degrees and worked pretty well. The sun protection is good too and helps keep the temp down better than exposed skin

BTW if it's really hot the beanie is fantastic if you can get water in there. I would spray cold water through a vent at Coz and actually found myself getting too cold, especially if I timed it with passing cloud cover. If such a thing were possible in COz