iTrip knock-offs

I was looking on eBay for a cheap iTrip since my cassette adapter broke the other day. I found a whole bunch of sellers offering mini FM transmitters that they advertise "are like the iTrip". Obviously, they don't look at good, but I imagine the technology is basically the same and they are a heck of a lot cheaper. Here's a link for one as an example. Has anyone bought one of these things? Are they total junk or will they do the job for listening to my iPod through my car radio?