Do satellite TV wedgie covers work?

I've been having problems with our satellite signal going out during the winter months, and the tech support guy on the phone suggested a satellite warmer... I'm a little wary of having an extension cord on our roof and heard that something called a "wedgie cover" (www.wedgiecovers.com) worked well, but I don't know anyone that has them and really don't understand how they work as it looks like it blocks the satellite signal. Does anyone have one, and do they work well?