I would also add that last I heard Onyx was probably violating the GPL if that is a decision factor for anybody reading this https://news.ycombinator.com/item?id=23735962

(please correct me if there were more recent developments)

If you have ebooks in a number of different ecosystems, perhaps kobo, comixology, kindle, adobe digital editions, pdf, actual epubs, microsoft word documents, then it's amazing having access to the official apps to read those file formats and connect to the online services.

You have access to the Android app ecosystem.

In the event you're not a fan of prorprietary Android apps, the BOOX also does F-Droid quite well.

(I use a mix of F-Droid and APK-Mirror sources.)

There seem to be a good set of mostly-works-on-eink apps on Android. Onyx's bookreader and note-taking apps (native and with better e-ink support) are also quite good. I've been disappointed by Linux e-book support on desktop, and the even smaller tablet space is quite probably worse.

Another available tool is Termux, and while no Linux replacement, it vastly increases the usefulness of Android devices.

There's no vanilla linux version of Libby, Kindle app, Kobo, Marvel Unlimited, Pressreader etc. At best you can maybe use a web browser for those which is a sub-par experience. For reading content Android is IMO better because there is general an app for DRM'd content. Linux doesn't have that and not all content can be made DRM free.

Have you used Linux on a mobile device? It is getting better, but it is not an enviable experience yet for your average user.

Take something like Spotify, for example. There is a desktop Linux client and an Android app. Guess which one works better on a small touch screen with only a bit of power?

vanilla linux doesn't have any good ereader apps

It's a plus when talking about a tablet-sized device with a touch screen - there are more Android apps for those use cases than Linux ones.

That will hopefully change with the PineNote.