I have a Boox e-reader and love it. It's an Android e-ink device so you get the benefits of being able to load android apps in, and you can put pretty much any ebook on there. That includes loading the Kindle App for Kindle books, other stores e-readers if you don't want to strip DRM, and free readers like FBReader to read anything you want. They also have a colour device which is interesting for comics.

They have a range of devices, and I have a Boox Nova with FBReader (e-reader but not open source unfortunately) installed from the google play store on the device and Calibre on my PC (which is a cross-platform open source ebook management system). You can use Calibre to load and manage the books on your eReader, and manage and organize a big library of books on your PC or laptop.

It means I can read an ebook from any source (including bought on Amazon, ebooks I've bought in other stores android app, or in any app if I've removed the DRM from the book, and ePUBs or Mobi from anywhere in FBReader or your preferred ereader from the Play store) on one good e-ink device. You can probably side load Android APKs but I haven't tried that. It's also touch screen so can take notes and stuff on it. And because it's an Android device I can also browse the internet and use android app like email etc. But it's an e-ink device though so the screen isn't designed for rapidly refreshing content; some Apps look janky on it and you can watch videos on it but they look a bit janky. It's good for reading websites, news apps, PDFs, email; that kind of stuff. Not really good or intended for video, or games. It's a superb e-reader, but with the added freedom of android. No amazon lock-in, no Kobo lock-in.

EDIT: Minor typos corrected