The $100 buys you massive improvements in usability with the 505. The Sony PRS-505 can read .RTF and .PDF files NATIVELY from its internal memory (210MB) and its SD card (2GB max) and its MSPD card (8GB max) all at the same time. The PRS-505 charges from any USB port. The PRS-505 will work as a card reader on almost any system. I use mine, and have never installed the Sony s/w.