For the weight and bulk to warmth, I usually pack something different such as light tarp, and extra clothes (watch cap, light puffy jacket and fleece underwear bottoms). The liner without a poncho (issue ponchos are heavier than you'd guess) gets pretty breezy and I've been pretty cold wrapped in one above 50 degrees. I know from experience that I nap better and warmer in those extra clothes than I do in a poncho liner.
It's a good piece of gear but I usually have better options handy without spending big money or carrying extra weight
