Don't care for it, for a bird dog.
I can see a possible use in extremes conditions in extreme places for dogs asked to perform extreme jobs regardless of climatic conditions IE people depend upon them...otherwise, I'd say don't hunt or go in the morning and evening.
Plus, I'm not a believer in dog vests in any manner for wear issues, heat, catching sticks, etc....fit would be the bugaboo.
I suppose tho that it depends upon where one hunts and the dog itself.
Some places, vests would be a safety issue I suppose.
Not sure how long these vests would stay cool before they become a heat sink, as well.
Seems to me that the makers of these vests are simply looking to expand into a hunting market...w/o being hunters.
That said, some will no doubt be purchased...maybe every minute.
Perhaps for a dove dog...who knows.