I love using my Remarkable as an e-reader. I've never been one to "write in the margins" because I like to keep my books clean, but this has been a surprising great feature of the Remarkable to me. I can write all over the PDF or epub and it saves as a copy (instead of overwriting the original).
If you're only going to read on it, and only white and black text, I'd recommend a Remarkable 2 instead as it's much cheaper.
An important caveat: I refuse to buy DRMed media, so all my e-books work on any device. They are almost entirely epubs or PDFs. If you buy stuff from the Kindle store then you won't be able to read them on the ReMarkable unless you strip the DRM.
After getting the rM2, I carried it. All of my notes are there, they're sharable from "the cloud", and I screen-share with it on Zoom calls for work when there's a need to diagram.
> What is so good about ReMarkable?
All of their products are, first and foremost, an "electronic paper notebook". They're designed to replace physical pen/pencil-and-paper. If that's what you want to use it for, you'll be happy with it.
> I would never use it for writing only reading white and black text with no images
I'd steer you toward an rM2 then, unless you absolutely need the backlight. They seem to be going for about $300 in like-new condition on the used market, so now is a good time to buy.
As for using it as an eReader, they work well in some cases and adequately in others.
PDF support is excellent - >90% of my eBook collection is uploaded to my reMarkable account in PDF format. It looks exactly the same on the device as it does printed, navigation works, and documents are easy to "mark up" using the pen.
EPUB support is... well, adequate. I think it's running a script in the backend the first time you open an EPUB file that converts it to PDF. Changing the font size does the same. For the rM2, this process could take a second or so for most documents and up to about 15 seconds for 500-ish page books. I've not empirically tested this, but the RPP seems to be much faster in this regard.
Note that DRM is not supported. That means you'll have to do the import/strip/export dance with Calibre if you have a collection of Kindle books to transfer.
There are also no integrated "stores", so you'll have to acquire your files elsewhere. I use Kobo for a lot of things. If Kobo doesn't have it - or if they don't have it DRM-free - I try to buy directly from the author. Failing that, I'll buy it on Kobo or Amazon then go download a PDF from libgen or similar.
I agree I think this is what it's doing behind the scenes. If you use the pen to mark up the book, it will be also saved as a PDF.
But for READING I would not go for a ReMarkable. They can't do Adobe DRM'd ePubs, they can't do library books and ePub support in general seems really subpar. Makes way more sense to get an Elispa or Boox model.