One advice: Seal its seams
This Bivy sack does what it's meant to, nothing more. It is amazingly light and is designed to keep you warm and dry while sleeping mostly ABOVE the snow line. i.e. when it is cold and snowy and rain is not your biggest concern. The biggest advantage is its highly breathable fabric (my experience, I see some controversy here), which is priceless as I use a down sleeping bag. Its disadvantage are the almost "transparent to water" seams, hence I strongly recommend sealing the seams for true water resistant (NOT waterproofness) If your are after water proof, Gore-Tex, and the like, this is not your sack.