Somewhat Hardcore Skier wrote a review of Black Diamond Mercury Mitten - Men's on March 19, 2013
These are the best gloves or mittens I have ever owned. They are warm, comfortable, waterproof, and breathable. I recently used these on a 0 degree day with the wind blowing at 30+ miles per hour. My hands stayed toasty warm for the most part. I could not even feel the coldest gusts of wind. There was a time on the lift near the summit where my trigger finger (the liner is a three finger mitten) got slightly cold, but nothing that bad. I could just move that finger in with the rest of them. They are rated from -20-0 degrees Fahrenheit, and this is probably true if you are talking about windchill. I was not wearing a liner that day. I think I would be correct with a liner.
My fingers also stayed dry the entire day. These wick moisture very well . I used to my fingers getting wet and clammy during even the coldest day, which only added to the cold, however this doesn't happen with these mitts. my hands stayed dry, and therefore warm.
I can personally say these a very waterproof. I tested them in my sink by letting the water run onto them. I was waterproof until I tried to run the water on the nose wipe on the thumb. It got soaked, and leaked into the mitten. I personally don't like this feature. It is not soft. I would rather wipe my nose on the shell of the mitt than the nose wipe.
All and all this is about a 4.5 star mitt, but I rounded up. I wish the removable liner was a mitten because it would make it warmer. I like the versatility. for extremely warm and wet spring skiing I can wear the shell and a liner glove. The shell is not comfortable to wear alone. I the high 20s and 30s I can wear a fleece glove and the shell. Between about 5 and 25 I can wear the shell and the removable liner, and lower than that I can wear a liner glove, the removable liner, and the shell. Great mitten! Don't think you can wear these under a jacket though. It doesn't work. I love the strap that wraps around your wrist. These mittens fit large.