Well, here’s my overall take.

The single best way to read an ebook, period, is moon+ reader. It just stomps everything else in terms of how you can adapt the reading experience. Libera is a not too distant second.

As such, I vastly prefer android based options, even for eink devices. I’ve tried kindle options, kobo, and looks barnes and noble nook, and a boox device. Nothing reads as well as my boox poke5 using moon+.

However, even the older models of boox devices aren’t cheap, so affordability is relative. I saved up for mine over a couple of months.

Second best reading experience is a tablet with a good screen, with moon+. You can essentially duplicate the contrast levels of an eink screen, and eye strain/screen fatigue become minimal to non existent. I favor a 7-8 inch device with at least a 2k×1.2k screen. Bigger screens, or less resolution, and you end up with janky text.

Third best is my older kobo with KOreader. Sorting through the library is a slow and annoying process, but the actual reading is nice. The native kobo reading software is meh, imo; and file navigation is worse. Maybe newer kobo devices are better at file management, I dunno. The screens are as good or better than Kindle options though. Really crisp.

Kindles, the only good thing is the screens. They render text very well. Everything else is just a bad experience, even when jailbroken (again, personal opinion based on my use preferences).

Since, up until recently, you didn’t even need an internet connection active on an eink device, software obsolescence was irrelevant. Security updates matter, but only if you’re going to be connected to anything because the formats involved and the lack of access to anything vital on them made it pointless to try and get into.

My eldest device, my old nook, still handles every file type it used to, still reads as well as ever, and it hasn’t had an update in over a decade.