I use it mostly to take notes in meetings and as a scratch pad. The small vertical separation between the surface and the screen and the replaceable tips make it feel _very_ close to writing on real paper.
For PDFs, I found the first-gen processor to be too slow to be practical. I doubt this has improved much.
The e-Ink screen can make flipping through past notes a bit of a pain. For reading/later reference, I prefer opening the notes on a real computer via the desktop app/cloud sync.
I did not order the ReMarkable 2 because I felt the upgrades were not worth the price. While I would love to have an eraser tip and USB-C, it _is_ still a very expensive gadget.
I also decided to preorder a 2 because the thing that breaks immersion for me the most currently is having to switch to eraser mode. I may still keep my 1 as well though, because as another commenter mentioned the biggest slow down is trying to flip back through notes on the device (even using the zoomed out view it can be quite slow with larger documents). I have been working through a few math textbooks and am actually looking forward to being able to have problems open on one tablet and the book on the other.
This beats them all. Yes, there are software quirks, some huge gaps in the system (cut and paste between notebooks), but it's always available with no friction.