heard about these so decided to try some as the price is reasonable. Wow. An odd sensation at first as it feels almost like they are cooling your arms more than being bare. But they work well and there's no more fumbling with sunscreen and becoming human fly paper on long rides. I have several pairs.
Slight preference for the black as the whites get very grimy quickly. And if you are super hot, you can wet them with water and it helps a great deal.
Combined with a castelli mesh based I can go out in 10 degrees more heat than before.