I've heard of other people doing well with those, but my experience is negative. It insulated my neck - the part of the gel closest to my body took on my body heat, prevented my own sweat from evaporating and cooling me there, and didn't exchange heat at all with the outer part of the bandanna, which presumably stayed cool.

What has literally saved my life more than once on the motorcycle is a cooling vest. I'm prone to overheating, and dizzy and confused on two wheels at 70 mph in traffic is not a good way to be. Mine is from TechNiche and those tend to be the most inexpensive. But, I've never used it at less than highway speed under a mesh jacket, so I can't speak to how it might work with less air flow. I know they sell a "velo" version and are popular among mountain bikers.