Received my ThermaKewl ($24.95 Cal Sport Touring) and tried it on the 86 degree day Friday. Worked great! I stayed cool for my entire 2 hour mosey around then watched my great nephews ball game (1 1/2 hr) game. I refreshed it, then went out for another half hour. It really helps keep your core down, and I was comfortable, not clammy, the entire time. I did find that my Underarmour heat shirt wicked the water down to my pants, so I got wet around the waist, but I'll take that over sweating in the sun. I would imagine if you take care of it the crystals in the vest should last for at least 2-3 years.
Next review is the kidney belt I just got! I cut my thumb on a broken glass, so it will have to wait until tomorrow.