Works as advertised
The temperature ratings were accurate and it was comfortable. Used the liner with an old Kelty mummy bag in Voyageurs National Park (Canada/Minnesota boundary waters country) back in September. Low temps at night were in the low 40s. Didn't have to deal with any extreme weather, just a little rain a couple days in. I enjoy the flexibility of the liner and I saw it as an easy way to keep my sleeping bag clean.