Its a long story about how I acquired my USGI 4-piece sleep system maybe post it one day. But I will say this, the outside green and inside black layer (did not have bivy at the time) but it was enough to keep me warm sleeping outside in Portland Oregon from December through Match of 2015, hopping freight from Oakland -> SLC (other sleeping bags were not) and during an unexpected Blizzard in Colorado. In the summer of 2016 I purchased a bivy and it along with the other two layers kept me warm and dry as I traveled close to the Canadian border and made my way across states like Minnesota, North Dakota and Montana including glacier national park which was dark, wet and cold.
If you plan to carry this in a pack the bag is probably just extra weight. The bivy is water resistant and NOT water proof. The thin green layer along is not enough to keep you warm in most weather, but the green along with the bivy for spring/summer weather.
Would I recommend this. its the warmest sleeping bag ever and not to much of a pain in ass to carry.