I have an REI magma 15 degree back and am not super impressed. If I had it to do over I would spend the money on something better. As the down moves around it gets a lot of cold spots.
I struggle with mummy bags because I get claustrophobic in them. I tried a Nemo Disco and like that it was a little more open but still light. I haven't used it much yet. So far I like it other than the zipper snags more than a quality bag should.
