According to that site you can downgrade the firmware (some people really disliked the various UI changes and the firmware is getting quite prescriptive)
You can also run your own homebrew apps so I found someone who installed KOReader which they claim is better experience than default reader especially for pdfs and also link better to personal cloud storage.
There's also ability to use locally stored Web Application Frameworks but I'm not 100% sure what the use case would be.
I think the usual consensus is Linux Mint (and its a solid distro) but I think the best advice is not to be afraid of trying different ones and finding out what works best for you.