Has anyone ever heard of or used these?
Miles Kimball Dryer Balls™ or Gaiam Dryer Balls?

How do they work? Is it, like, magic? Do they need to be replaced every few loads or are they good forever? I've read what the sellers say, but I'm looking for non-biased consumer opinions.
Also, has anyone seen any that are actually made in America -or perhaps somewhere other than China?

Thanks!!

A couple of tennis balls thrown in the dryer works well for fluffing stuff like comforters and towels(Low and medium heat only, not high) so I imagine that an item more specifically designed for the task works even better.

I bought some at the Seen on TV store. My clothes came out of the dryer full of static. I threw the dryer balls in the trash.