I recently got a Sony D-NE715which offers similar features. I understant Atrac3 has a similar compression rate to MP3 (~10:1). Atrac3 plus offers about 20:1 compression. Both can be encoded at 2 or 3 different bitrates.
Personally, I am sticking with MP3. I can have the music from 10 of my music CDs on a single disc. I use readily available freeware programs to get the music on to a CD R/W (e.g. CDex) and create playlists using WinAmp.
I am really pleased with the product. My only slight complaint is that the screen is too small to display enough information about the track names etc.