If you really only want to spend 20 bucks on the solution, the next time you are at Harbor Freight:
http://www.harborfreight.com/12-volt-rubberized-heater-with-fan-96144.html
It is the same as one of your links. Go plug it in, and see how hot the cord gets after 5 minutes. That should tell you about the rest of the quality.
B.
