I switched to the HMK Pro Boa Focus II this season. This boot is far superior to Klim Adren GTX for riding support and the lack of an elevated heal gives an advanced rider better contact with the running boards. Per previous comments the boa system is the best aspect of these boots. Then add two adjustments and it's excellent for creating a custom comfortable fit.
We found that there are only two ways you get wet in this boot when snowmobiling (I'm not talking about walking around in a 6" puddle like the rediculous waterproof field test). You get wet from either your own sweat or from snow getting past the lacing area or over the tops then melting from your body heat. By wearing a quality pant with a good gator so that snow can't get over the top, making sure that you've got the tongue placed so that no snow gets past on the lower section of the boot, and then by wearing a quality moisture control sock you can completely avoid moisture problems in common day to day sledding.
Each person has different levels of perspiration so experimentation of socks and tightness of the system makes all the difference in the world for comfort and sweat control. The HMK is the best performance boot I"ve worn and now we've got it figured out so it's also warm, dry, and comfortable. Would also love to see the tongue section closed to the shell to completely eliminate snow contact through the bottom half of the boot.
Tough (my Klim's wore a fur patch on the fabric section after two rides), better support, easy custom fit, dry, warm, all make the HMK pro boa focus II a superior performance snowmobile riding boot.