· Why doesn't it play MP3 CD-R discs?
Actually, it will: If you use your PC to load the contents of the MP3 CD-R into the player ahead of time, it will play the files just fine.
It just doesn't have a CD mechanism built directly into the player. The designers felt that having room for two shock-mounted hard disks was much more useful than having a CD drive in the player.
Yes, there are other CD player products on the market which will also play MP3 CD-R discs. Sure, they're cheaper, but they'll never be as good as the Rio Car player.
The whole point of the player is so that you can have your entire music collection in the car with you at all times, without the need to shuffle CDs in and out of a player or a changer.
CD-R discs are limited to about 650 megabytes of data. At a mediocre encoding rate of 128kbps, that gives you room for about 10-12 albums' worth of MP3 files on a single CD-R. This is no better than a CD changer, and you'd still have to carry a big stack of discs around in order to have a truly large variety of music at your disposal. The Rio Car, on the other hand, allows you to go completely without CDs of any kind, and can store vast amounts of music.
There are also issues with the access and index times of MP3 CD-R systems. When you first insert a CD-R into one of these cheaper players, the disc must be indexed, so there is a pause as the player reads the information. For most, there is also a pause between songs or when you skip forward to the next track. These operations are essentially instantaneous on the Rio Car.
Finally, the advanced database features of the Rio Car, such as searching, hierarchical playlists, filters, bookmarks, etc., are all made possible because the player has hard disks instead of the read-only medium of a burned CD.