Do you write on it? How is the stylus pen? Is there a lot of lag/latency?
You do, yeah; the front of the tablet has a textured surface to make it feel closer to paper than the slippery effect you get from a glass screen. The back has that too despite not being something you write on, so it's got a nice feel overall.
The stylus is good - solidly built, pressure-sensitive, attaches to the side with a magnet, and comes with a pack of replacement nibs. The base model only has a sensor in the nib, but you can pay extra to get one with an eraser on the flat end.
Lag-wise it's pretty good - noticeable when compared to real paper, but not enough to throw off handwriting or drawing. This is my first e-ink device so I don't have anything to compare to, but I found the panel resolution and digitizer precision quite impressive.
I know 3 people with that same tablet. They all seem to really love it. For me, I have no issue using my iPad & pencil but I get it for those who can't deal with the smooth surface of the glass.
The paper feel is a nice bonus, but for me the real appeal for me is being able to avoid another smart device with a big ecosystem that wants to do everything - I'm at the point where the information age is beginning to take its toll, so being able to nix that stuff out and better control the extent to which app stores, notifications and social feeds run my life is a boon.
Though the hackability was the clincher; Remarkable are one of the few companies who take GNU Public License compliance seriously, so you can get a valid SSH root login straight from the settings menu. I don't usually touch mobile devices in terms of software development - too much of a mess in terms of packaging / signing / sideloading - but this one has an open enough approach that I was able to get in and write my own launcher for it without too much strife.
If there was an equivalent e-ink phone based around the same ideas I'd be all over it, but unfortunately the closest equivalent goes in so hard on the simplicity that it ends up being more locked down that your average iOS / Android. Maybe someday...