If you're looking for a fart sack that comfortably handles -10F this is a great if expensive choice. The problem is that vendors such as REI frequently list its extreme rating, -22F, as its comfort rating. Unless you are an extremely warm sleeper or an ultralight fanatic who likes to wear your down parka inside your bag at night to shave ounces, do not plan on using this bag at -22F.
The bag is not the problem, the problem is that it is common in the United States to use comfort ratings and in Europe to use extreme ratings. The Valandre web site clearly states that -22F is the extreme rating. I have used this bag in the minus twenty range and it is true I did not die, but neither did I sleep well. Caveat Emptor.