For me the killer anti-feature of reMarkable devices is the limited storage. I have way more than 64 GB of ebooks and PDFs (lots of full-color tabletop game books), so anything that has both such limited storage and no SD card slot is off my radar.
It's not good as an e-book reader regardless of how much storage you need. It renders epubs to pdf on the fly (so changing the font size induces a long delay in a big document, for instance). The documentation even tells you it's not a good ebook reader.
Do you need to have hundreds and thousands of pdfs on a reading device? How fast can you read?