I work outdoors on the west slope of the Colorado Rockies . I purchased this bag to solve the 20 below zero weather that comes along now and again. The bag works well, sometimes ice accumulates around the face area, the addition of fur around the snorkle area solved that. Padding under you is needed if you are sleeping on the ice or snow. As to the bag being too much for a mild night, just unzip it and let a little air enter . Well worth the investment, if you are serious about being in the cold .

I got this bag for Denali. I wanted to test this out in the So. CA mountains. Let me just say, if it's not below zero, this thing is too hot! It got down to the low 20's F sleeping on snow. I was sweating. I then zip the bag down a bit to cool off, then I was freezing from the sweat. This thing is hard to regulate! It was a constant battle to keep comfortable. I'm confident that it would work perfectly in sub zero temps. I do like the fact that it has plenty of room around the upper body. This made it really nice to move around in the bag. I did notice it takes a bit longer to warm up due to this extra room.
One downside is the bag only comes in long. I guess this is good if you need to sleep with your boots at the bottom. I also notice that feathers tend to come out of the seams quite frequently. So the long-term durability is questionable. I might just have a zero degree bag in a couple of years.
It comes with a huge compression sack. Even with this compression sack (quite large), it would not fit in my sleeping compartment in my pack. I later purchased a granite air-lite compression sack (large) which worked a lot better. It takes more time to stuff, but it now fits in my sleeping bag compartment. The watch pocket is a silly gimmick that just adds weight. All in all this is a superb bag. Just make sure it's very cold were you intend to use it.