Before we got one for the family, I noticed that several of our friends had laptops that would shut off after 30 minutes or so due to overheating. Apparently many laptop cooling vents get clogged with lint (makes sense considering how they're normally used). In addition, some of the vents are blocked when a laptop sits on the lap.
We got one of the cooling units but no one in the family ever turns it on. Even so, it serves it's purpose for providing a flat surface so the ports are not blocked as my kids/wife use it on their lap or couch or rug or ....
Ours is a Rosewill. It's mostly metal and reasonably well made. For the small cost, it seems worthwhile.