I've got a Reactor liner and bring it along at least in the truck for insurance. I dislike using it because it sort of clings to me whenever I move around and feels a bit constricting...though I also don't really like mummy bags period, so that is probably part of it.
I'm not sure how much it really helps, but I've had a couple nights where I would've taken any bit of warmth I could get, so I still bring the ol' liner along. I think they claim 10 or more degrees, but I'd wager that is a stretch.
Based on weight and bulk, I've been interested in a light down quilt. Seems like it would be warmer, more comfortable, and more versatile. Pricey though, sonthere's that tradeoff to consider as well.