I'm trying to find an ultralight sleeping bag which isn't too expensive.

So far I'm thinking of getting one of these. They seem to work well, and are only 3oz, and fit in the palm of your hand.

I've heard they can produce a lot of condensation, as they are not breathable, but since they're pretty large it could fit other liners, like maybe a poncho liner or some other thermal liner.

AMK also makes 3 different models of this SOL emergency bivvy, with the "escape" series being breathable but slightly less warm and much smaller of a fit.

Has anyone tried these? And what are some other ultralight sleeping bag options that would keep someone warm in 30F.