Oh, that's interesting. Pretty much exactly what I'm after! It has better specs than my phone. Says it runs Android, so I assume it's reasonably "open".
More or less. There are ways to flash arbitrary android builds on Boox devices, but you'd lose a lot by doing so.
The Boox software is actually pretty good. It does a lot to make non-e-ink optimized android apps work well on an e-ink screen, and lets you tweak it as you see fit, so you can adjust contrast and whatnot to make text and elements work. Its not always flawless, but it does work.
The in-built reader application is very good, particularly when it comes to annotations and whatnot. It has a dedicated notebook feature, but I've never been one for hand-written notes, so I don't really use it. And if you don't like the built in one, you have the advantage of being able to load any android reader application you like. Google Play Books, Kindle, Nook, KOReader, MoonReader, whatever, they all work.
Now, in the spirit of full disclosure, I have the larger, A4 sized Onyx Note, and use mine primarily for sheet music. But it works very well as a technical paper or programming book reading device, in a way that kindles and other smaller readers are insufficient. So some of my experiences might not carry over to the Palma. But I can't imagine Boox going through that much differentiation of their product SKUs to the point where this comment will be wholly accurate.
https://onyxboox.com/boox_palma