I bought these for winter camping in Michigan(with my Boy Scout son) and after reviewing dozens of others (including the Alti), I figured that at 20% off of the $86 price tag, if they aren't all that warm, then I'll give them to a young family member whose fingers don't get as cold as mine do. As it turns out, I cannot imagine a warmer, more comfortable pair of mittens. With the trigger finger design and overall warmth, these remind of the leather shell, lambs wool-lined mittens that my dad wore in WWII as a Merchant Marine sailing at times during winter storms that required heavy-duty warmth.
Since, like everyone else, I want or need some dexterity at times, I simply ordered a size up and where liner gloves (O.R. PL400's) beneath and I am literally covered. My liners slide in and out with ease and mate perfectly with the Mercurys. For now, I can only imagine that my particular combo will keep me comfortable well below zero (Farenheit).
Also a tip/trick, if I only need the liners for a time and don't want the mittens exposed and dangling from their "idiot cords", I crafted a way to keep the mittens warm and secure inside my jacket by adding Nite-Ize size #2 S-biners to the loop ends of sport eyeglass Chums, then attaching the mittens to the biners and hanging all this from around the collar of my base layer. This set-up makes my coat a little puffy around the chest area, but it keeps me and the mittens warm and protected from the elements.
The bottom line is that the Mercury mitts are incredibly warm and well-made at any price. To Black Diamond, thanks for a product well-done, but please continue to keep the price down, I still have my wife and kids to buy these for.