Kobo's devices let you bypass the account signup via a single option in a config file. Whether you do so or not it's easy to install koreader and start writing plugins for it. You can also hack on the linux OS they use
You can also sync to your own library - eg calibreweb.
It’s not too disgusting, and over-the-air is nice to have.
Yep, there's a plethora of tweaks and stuff out there to mess with Kobos to make them your own, and it's not hard to do.
Been super happy with my Kobo Clara.