That is very interesting! I've wondered if feathered feet stay warmer, but I've never seen any actual information until now.I also want to point out that those feathers come in handy on feet where i am too. I have some poor clean legged birds that have fractions of their toes left and most of the lucky ones are missing at least a toenail.
My birds with feathered legs and feet have never lost so much as a toenail to the cold.
(I have never had a chicken lose a toe, comb, or anything else to frostbite, so I wasn't in a position to make comparisons. I've mostly avoided feathered feet, because I hate them being muddy, and I've dealt more with muddy conditions than with extreme cold.)