Downside is no backlight which many users tout as an improvement, or praise it as a minimalist perk. I don't really agree, but it does mean that the ink surface is closer to the pen so there's less parallax error. It makes it less usable as an ebook reader though, for example on a flight you'd have to use the blinding overhead lights.
Sure the price is comparable to 20+ notebooks. I think if you actually use notebooks, they're good. If you don't, it's questionable whether it'll change your habit. It also doesn't replace the satisfaction of a nice ink pen on nice paper. I have a collection of fountain pen ink that I've used since university (for years of daily lecture notes which is more writing than I'm ever likely to do again - we're talking up to 20 A4 sides a day) and the bottles are still practically full. So good writing equipment can be very economical. There are other issues like no colour (on mine) and PDF support is still ropey.
I won't say they're bad solutions at all, but just that they brought no actual benefits for my use cases so there wasn't a reason to put up with their downsides. The downsides are relatively minor, though. For me, they are cost, the need to charge yet another device, and the inconvenience of the form factor (you can't tear pages out to hand to someone else, they rigid tablets instead of flexible paper, writing on them isn't the most pleasant thing, etc.)
Though when at home/office nothing beats paper and the possibility to visually have multiple pages side by side. Any research article I want to work through I print out, and I buy more paper books now than before I bought the remarkable. Paradoxically, the remarkable helped me realize the incredible value of paper.
I use a Boox E-Ink tablet with the built-in handwriting notes app. It exports to PDF and I can copy everything to my Debian machine via ADB. I absolutely love it. E-Ink is close enough to paper for me, and the EMR (Wacom) stylus is close enough to a pen for me.
The device was worth every penny, even before considering the other uses for it.
A few months ago I sold the rm2 and got an rm3 "paper pro" and despite the $$ it has ROI as a daily driver (alongside Obsidian running on my M4 macbook air).
To be more specific, the ReMarkable 2 had a wildly inaccurate pen tip, but only on like the bottom 1/2 to maybe 1/3 of the screen, which was enough to completely destroy my desire to use it at all. On top of that the software is pretty meh. It wasn't bad so much as it was minimal to the point of being harder to work with than real paper. The UI was clunky and slow. Any real advantage to digital nature (built-in OCR, sorta search) was so poorly implemented that it wasn't worth it.