I have tried various light weight down jackets and all seemed to have either to much or too little insulation. This fills the gap nicely. Fits as expected in my normal size - large - and has a fairly slim cut so fits well under a shell, etc. Only complaint is the weird zipper, first of all it is on the WRONG side, and second, the two way zip is a PITA and gives some difficulty if not engaged perfectly. Maybe my sample has a flaw as I am pretty sure it had been purchased and returned before, as the plastic packaging was fairly shredded. If zipper problems persist, I will be testing Mammut's customer service - once it warms up here.
Use it just about everyday, everywhere. Not bulky like some down jackets but still warm. Sleeves and overall length are perfect. Definitely usable for basecamp or at the peak but I would hesitate taking this on the trail with a pack because I don't want a scratch on it. Mine is not poofy in front as some have stated in reviews. Left sided zipper is something to remember when trying to remove it quick.