I currently have the remarkable V1 and have used it "extensively" (211 pages in 19 notebooks, plus 10 books like PHB 5e, CISSP guide book, and various other nerd things and white papers). I am super happy with the product as it solved my use case of wanting to keep my notes handwritten yet on my person without having to carry around multiple notebooks. I also love the fact that I can have a notebook that goes from us legal lined paper background to large grid background, and back multiple times.
It's PDF capabilities are fine, and you can write on the pages which is nice, but I've not really tried to access any of these notes outside of the device. The did roll their own cloud sync capabilities though so you can use their apps on devices for that. There's also the 3rd party options that exist for that too.
As mentioned by jagraff they expose ssh and allow you to login as root. The whole device is a linux machine so if you want to setup syncthing to run on it you can[1]. If you want something else like zotero, or google drive, I suggest checking their wiki[2] and the github repos[3] dedicated to curating some of the stuff written for it
TLDR; Super happy with remarkable v1. So happy pre ordered V2. It gives you root on a linux box.
[1]: https://github.com/evidlo/remarkable_syncthing
[2]: https://remarkablewiki.com/tips/start
[3]: https://github.com/reHackable/awesome-reMarkable