ATrac is just another compression format. It's been around for a long time, as it is behind the scenes in all versions of minidisc, as well as Sony's current ill-fated attempts to dethrone the iPod.
It has decent sound at lower bitrates, but it's not going to blow your mind or anything. It is way too proprietary for my taste, and last I checked the Sony software had all sorts of limitations...
For instance, it will only let you transfer an MP3 onto 3 discs. Yes, you heard me right, Sony wants to put draconian "rights management" onto your own MP3's, and limit how many copies you can make of your own files.
If you're trying to save money, get a plain portable mp3 player. You can record MP3's at lower bitrate VBR and they'll sound identical in a car environment, and you'll be able to fit the same number of songs.