They work just fine, especially in a car environment where "fidelity" is really not all that important. You can also get corded versions that plug into the ear phone jack of your MP3 player then the cassette end goes into the car's player. They work fine as well. The fidelity is about the same as with a tape, not great but again you're talking about inside a car.
Overall these are a great solution for any sound system that doesn't have any audio inputs. You can sometime find the corded version at surplus places for $5 or so, for example;
http://www.allelectronics.com/make-a-st ... R/-/1.html
There are also cheap FM transmitters that plug into the MP3 headphone jack and transmit to the car's stereo system via FM. People tend to have varying success with those. Some times they work great, sometimes not. Depends on the transmitter and the car's reciever.
There are of course "better" solutions but they all tend to cost considerably more $$$.
Decided to search to see if such animal existed, and ... it does !
