Great for under 30...
I don't get cold that fast, but found that at the end of an hour long ride my feet where getting extremely cold in 30 or colder weather.
I was using the capo sock shoe covers and wanted something for the colder times. These work really well for me. My feet stay warm but not to warm that they sweat.
I'm a big fan of the open bottom, let's me walk around without a problem.