Brazilian Government just released a great public library of e-books: https://meclivros.mec.gov.br/
An Android e-ink reader would be perfect for it. And I'd use kindle app to read my kindle ebooks. But I don't really see people using them.
For actually reading ebooks, I'm using Koreader instead of the built-in reader because I find the UI a bit easier to get my head around. I mostly use it for PDFs related to classroom learning, but have the odd epub knocking around from project gutenburg etc.
It has Google Play support, so I can use the Libby app to access my local library's ebook collection (including offline access to travel guides - so useful). I also use the Sefaria app to read Hebrew scripture (also supports offline). These apps tend to use the battery faster than Koreader and having scrolling controls instead of page-turning controls is a bit of a pain, but quite manageable.
I haven't tried the Kindle app, but I'm sure it would work fine.
It’s like an entrepreneur with social media marketing skills came across a container full of really cheap small eink displays, then designed a product and marketing around it.
The build quality could be better, but there doesn't exist a similar product with better build quality.
Can you build a DIY version that's significantly cheaper?
Well, this was my thinking for getting one, we shall see when it arrives :P
Edit: Also you can choose to install a nice open source community firmware
It's 10 inches, which I find to be a bit too large for an E-Reader. But for surfing the web and note taking this is a terrific device. Boox has smaller Android devices.
I don't know if I love it yet but I read seven ebooks in a month on it, so I guess it's been a good purchase. The android kindle app has a neat smooth scrolling feature that works really well.