I'm considering these for the summer. Its as someone (Butch?) said, it might not feel like its working during the day, but at night, after work is done, you'll know.
How good is it to have AC in the truck to cool down between jobs or what not (I don't have it in my trucks)?
It would be interesting to take your body temperature before the cool vest and after. A change of half a degree could be significant, and I could imagine it.
Often a bigger removal, for the climber, is shaded until the spar take-down, later in the day, in greater heat. I can see this helping.
I'll try to work the shade/ sun in my task planning. For example, when I had to end-weight reduce a big conifer for 6 hours in the tree, I started on the south in the morning, and worked clockwise, using the sun and shade to my advantage.
In a total sun for the groundies type of situation, I have a EZ Up shade canopy. Good for splitting firewood in the summer, too (firewood processing area is total sun at my place).