Own a size medium Montbell Alpine Down jacket. Purchased it just to have a nice looking warm jacket for non-active winter pursuits: birding - day and night. Features, fit, and finish are exceptional. This jacket is so very warm. Winter has been warm this year, but some wee hours in December had sub +5 deg F mornings. Jacket kept me very warm with no activity. Forget about using it for anything that gets the blood pumping - it would cause a great deal of sweating, IMHO.
My only complaint about the jacket (and I knew this going in) is that it lacks a hood. Any garment with this much insulation should really be a parka with a hood, or a shorter length hooded-jacket. I don't ski, so maybe that is an application for a very well-insulted hoodless jacket. It might have an application for Alpine (not Nordic) sking - though it might be too warm for some downhill ski areas.
The only other thing to mention is that you'll look like a Pillsbury Pop'n Fresh Doughboy or a Stay-Puff Marshmellow man wearing this thing. It is very "poo-fy". Figure that it has almost as much down as in a WM Highlite short sleeping bag (7oz vs 6oz for the jacket), but it's all in just a jacket's dimensions. The down really lofts in this thing. And while only 6oz of down, for example, the sleeves' outer diameter rivals my 25yr old Eddie Bauer Kara Koram parka (supposedly good to -40deg F, double-layer offset box quilt - used infrequently over the years, so down is still pretty clean and lofts well, almost like new).