Light, stuffable, breathable...great to throw into the pack or to wear straight out of the gate. I bought this to put in my pack during ascents so I could wear it between my baselayer and shell on the way down when backcountry skiing, snow-shoeing, or while doing some ice climbing. However, I haven't used it for any of that yet...I've used it for camping, riding, loafing, and for running the dogs and it's lived up to every expectation so far...warmth without overheating or the bulkiness of some of the loftier down jackets. I compared this to Patagonia's down sweater and liked this one a bit more because it was less bulky around the collar and more fit around the waist. If this sweater fits too snug around the middle, I think the Patagonia version would be your baby! I'm 6'0", 155, have a 15.5 neck, 32 sleeve, and a 38 chest - I bought the small and it fits great (snug but not overly tight - great for layering). Can't wait to get a MontBell sleeping bag now!
Compare this to the Patagonia down sweater!