Whenever I see any YouTube hikers prepping for an early start, it seems many of them say they are bringing a sleeping bag liner (usually the Sea-to-Summit Reactor) because "they say it can add, like, 20° more warmth to my bag (or quilt.)" Yet I never hear anyone ever follow-up and say whether or not that has truly been their experience. Any hikers who do a post-hike gear review will say they used and loved their sleeping bag liner because it kept their bag cleaner, but those are the lightweight "travel" ones.
I'm genuinely curious if anyone can share their experience with these Reactor liners, and especially if they think it's worth the weight and [considerable] expense. It looks like these things range from 8 to 14 ounces, and cost $60 to $70.
I'm not considering one, just curious.