I like these a lot. They are thick and lined with nice long velcro straps to tighten and fold flat for storage(!). I'm not sure what temperatures they are good for but this winter we got down to 23 deg F with no issues.
What more can I say? They are cheap and easy to put on. My pipes did not freeze. Would they have frozen without these things? Probably not. But better safe than soaked.
They were small and i didn't think they would fit my spigots but they did. I think they should have been made an inch longer; then they would have been perfect!