I once had a Sony e-reader, it was great for purpose. As has been suggested, it's best for the ePub format, less good with PDFs.
For whatever reasons, the landscape for eReaders has consolidated into two brands -- Kobo and Kindle.
The situation may have changed since I last checked it out, but last I recall Kindles were optimised for Amazon content and didn't do unlocked ePubs very well.
They also used to be cheaper, but as I look now the current price on an 8" Kobo is $50 more than I paid for my 9"Android tablet. That's if you buy locally. If you don't mind going offshore there are dozens of offers at less than $100 on aliexpress (
here's one example).
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Evan Leibovitch, Toronto Canada
@evanleibovitch / @el56