I also own a reMarkable 2 since last December and the fact it is not a light source makes it valuable when you spend almost all your waking hours staring at screens.
For me, the most useful trait is that it gathers all my note in a "physical" gadget rather than being scattered on several laptops/smartphones/notebook.
I have one as well. For me the killer feature is the ability to copy/paste your own handwriting.
I'm on the device 6 of 8 hours in a day, constantly taking notes of my meetings and conversations. Frequently I write sentences in the wrong order, and have to rearrange them for logical/linear understanding.
Sure, you can do that on a Slate or iPad, but neither feel or sound like you're writing on real paper.
The fact that it's a single-purpose (ish) device, and that it feels and works so much like real paper.
It's like being able to carry an infinite number of infinitely long paper notebooks with you.
I used to get through about one paper notebook a month, and couldn't find notes I'd taken 3+ months ago. Now everything I've ever noted is available with 5-30 seconds of searching and paging about.
The fact that, if I've written a bunch of notes in the wrong place, I can cut and paste them elsewhere is something I use every day. Everything is so much more organised.
Also, and it's definitely NOT designed as an e-reader, but if you convert your ebooks to fit the screen, it's approximately the size of a hardback book page, which I find miles more comfortable to read from than my Kindle.
Would you mind saying what you find most useful?
I have an aging iPad and would very much like to replace it with an a-ink device because I don’t like staring at a light source.