I bought a pair of the Kenetrek mountain extremes. I like the design and was surprised to see how much I like the taller tops. They make side-hill hiking easier and offer better support. On flat ground they feel great, but do some climbing and they destroy my heels. Massive blisters. They're stiff boots and I paid a lot for them, so I've been committed to breaking them in. I feel like there's no heel cup in the back. It's just flat. I've done probably 10-15 hikes with them this summer, often going double or triple layer thin socks. This last hike i covered my heel in moleskin and that helped. At first I would only last a mile or two with some steep climbing before the blisters started. Now I'm getting up to 5-6 miles, but certainly not without pain. I bought their weather sealer hoping that would soften them up, which it did a little. Still not good enough, especially if i expect to wear them for a full week of hunting. I read one review where someone said it took about 50 miles before they broke in. He wasn't kidding! I'm probably in that range so far. I'm now hoping they break in before elk hunting in Sept. Starting to consider getting a different brand as backup.
Now I know why when someone finds a brand that works for their feet they stick with it.