I've never used one, but I know there is a pretty long on-going thread over at RVNet about them.
Reading through them, it looks like some swear by them, and others purchase one, use it for a camping season and move up to the Honda.
If you're only going to be using it as an emergency, then it'll save you a bunch of money over the Honda, but if you plan on using it regularly, then I'd save your money and go with the Honda.
Good Luck
Pat