With a jailbroken Kindle you can, for instance, install koreader[1], a feature-rich alternative ebook reader application that enhances the somewhat limited capabilities of Kindle’s native reader.

For instance, with koreader you can open djvus, epubs, fb2 (if you’re onto those formats), but what makes koreader especially appealing to me is that it is a far better pdf reader than Kindle’s native.

Or you can look for a pool of available hacks[2] that make Kindle’s overall usage far more suited to your own particular needs. One example is the screensavers hack that allows you to choose either to use your own images (somewhat interesting if you’re onto customizing them to your tastes); or you can, as I prefer, to use that last displayed screen as the screensaver, as this allows you to keep a book’s opened page in display while you are taking notes or doing some other book research related task.

Some of these new features are now so essential to my Kindle’s experience that I can’t imagine myself using an original one without jailbreaking it. Also, I have my Kindle since 2015 and I’m in no hurry to get a newer or more capable model. As it is, it is very tailored to my academic needs.

[1] https://github.com/koreader/koreader

[2] https://www.mobileread.com/forums/showthread.php?t=180113