Rating: 5 / 5
...this jacket is SO much warmer than it looks.
Minimalist on features, but "maximist" on warmth, and it doesn't look half bad to boot.
Every bit as good as the ThermaWrap vest, but it keeps your arms warm too (cf. see review of the Thermawrap vest here which contains more details
Would it keep me warm down into the mid-to-uper teens like a prev. reviewer wrote? I don't know, but I have used the sleeveless ThermaWrap vest under an unisulated Anorak shell and, other than my arms, was warm at 26 deg F for 20 minutes. So, the jacket would do as well and most likely a bit better. Upper teens for me...hmm...i'd "gamble" on that for a weekend trek.
I can only compare it to the BMW Cocoon Pullover. The Cocoon is ~0.3oz lighter (based upon Mfr. claimed weights for size M) and is warmer, IME (in my experience). Just for fun (yeah...i sure know how to party!!!), i tried them one-after-another outside, Thermawrap first (perhaps(?), a slight advantage) for twenty minutes. some wind, but not windy, nor calm (sorry, i don't know the wind speed - i haven't bought one of those gizmo's yet). Temp was ~28 deg. 20 minutes standing around & walking slowly, checking out birds and plants in the back yard, and watching the squirrels forage and the stray cats stalk them. Face was feeling, not cold, but was feeling the cold. Body and arms were warm. Felt like I could wear this all day. Was careful not to move too much and overheat. Went in and changed. Now the Cocoon; every bit as good as the Thermawrap Jacket - probably better/warmer - my very subjective impression. I know, not much of a test. Haven't done much cold weather trekking this winter (sprained right knee). All i know is that i wouldn't want to do much on the move hiking with either of these - overheat too easily that's for sure. Obviously, if they had to be worn while on-the-go due to very cold temps, the full-zip of the ThermaWrap would help expel more warm air than the half-zip of the Cocoon pullover though.
If you need a full-zip jacket, then the Montbell is the way to go. If you want something warmer, or prefer pullovers and Anoraks to jackets (like i do) then the BMW Cocoon is your choice. Either way, you can't go wrong.