I have the 256MB black model http://www.shirocorp.com/products/mp3/mp3_sx.html . It's actually pretty good (OLED colour display, FM tuner, Equaliser, USB2.0 support... etc.) except that it doesn't handle any kind of playlist whatsoever.
One the main plus for me was that it runs on a single AAA battery and comes with SD/MMC expansion card support. I've tested it successfully with a 2GB SD card but without playlist support, it'll be difficult to find the song you want.
Overall, it's very light and sturdy (hey, it's flash!)and if you can find a compatible hand-strap (unfortunately none bundled), this works very well for gym. Cheers.