So I went on a 50 mile ride today and put these on at about 36 miles, as the temperature climbed up to 90F and wore them the rest of the way as it got hotter, about 97F.
First off, they're white and extend from my wrist to almost hit my armpit -and I'm a 5'9" guy. They were definitely running up into the short sleeve of my jersey.
As far as the cooling effect, it was a weird, kindof chemical effect. well duh, that's what it says. I wondered if lathering up with Vick's Vapor Rub would have done the same thing, but I'm not going to try that. It was a similar feeling, though, so I'm not sure if they actually cooled my arms or just gave me that perception. The cooling was most noticeable when I first put them on, or when I stood on the downwind bank of the river.
Other effects besides cooling:
Sun protection: undetermined. I had a tan before and after the ride. :/
Looks: Of course you'll get looks. Who wears long sleeves in the summer? and you'll get to brag about the technology.
Visibility: I think these increased my daytime visibility, especially nice for riding in traffic. A blazing white arm is easier for auto drivers to spot when you make signals. Night visibility will improve for the same reason, but they could have done better by providing a reflective band at the wrist or something.
Overall: offered some cooling sensation, didn't make me hotter, increased visibility.