This is a device category I have very little knowledge about, but I have a growing collection of PDFs and ebooks and I'd love to have a light weight device to read them on.
GPL is the one that requires you to freely publish your changes to the source code for others to use. its not based to make it much harder to maintain the device once the manufacturer decides to drop support.
These look really nice and exactly what I'm looking for. Its funny, my SO is laughing because she used to sell these at Borders book store years ago, she said they couldn't compete with kindals at the time. Looks like they're doing well now though!