This is a great vest for all around. It will keep you plenty warm and works perfectly alone or as a layering piece. Packs down into its own pocket which makes it great for traveling or as a pillow. Have not used in high aerobic activity but feels it might have a little too much puff volume relative to Marmot's Variant (or the like).
For sizing, I am 5'10" & 155lbs and small is perfect for me.
This review was written in the old system and had content requirements that are different than reviews written today.