I originally purchased this cassette adapter to listen to CD's in my Neon which did not have a CD player. This served its purpose well- great sound quality, the cassette was not loud in the cassette deck as a previous one had been, and I was finally able to listen to CD's in my car during the commute.
Eight months ago, I traded in the Neon for a Jetta which had both a CD and cassette player, so the cassette adapter wound up collecting dust along with my old cell phone and other assorted items in my electronics graveyard. But this week I purchased an iPod, and I also got an iRock FM transmitter to listen to my MP3's at work and during the commute. Unfortunately that is not the best product in the world. I contemplated exchanging the iRock for a Belkin FM transmitter, when it was suggested to me that I try a car cassette adapter. I dug through the electronics graveyard, and almost thought I had thrown this out when I found it. I plugged it into the headphone jack of the iPod, then played the cassette on my stereo. The sound quality is excellent on this as well.
This is an excellent product if you have a car with only a cassette player, and want to listen to CDs, or if you have an iPod and want to listen to MP3's cheaply and easily.
A piece of advice, though for those who need the adapter for their CD player: you may want to opt instead for an actual car pack, which has a cigarette lighter adapter for the CD player, otherwise you'll be burning through the batteries like crazy.