IMO they are not the kind of thing to be wearing if you are looking for coolness. I’ve got the cold weather HAIX and they are big waterproof monster boots; standing in streams, 10 inches of watery mud, slogging through deep heather…
I think the difference between the summer and winter boots is the weight and coverage with leather.
I have worn them in wet summery conditions without drowning in sweat, but if I wanted cool feet… they’re not the first choice.
Lowa mid desert boots appear to be the footwear of choice amongst a couple of people who work in hot places for large sums of money.