I’m a heavy KOReader user and absolutely adore it, but I think it definitely trades user-friendliness for power and flexibility. The Kindle proprietary store has a far more user friendly UI imo, though it’s getting progressively worse (and the fact that kindles now default to showing you the store pisses me off to no end). KOReader plugins really close the gap though.

I think the only proprietary software companies with any shot at longevity are Japanese companies. First Japan leads by far the ranking of oldest companies in the world (https://en.wikipedia.org/wiki/List_of_oldest_companies). Then we have actual software like Zelda Breath of the Wild which is a technical marvel comparable to the original Rollercoaster Tycoon considering how well it runs on the severely limited architecture of the Switch.

I think this boils down to profit not being the only driving force for these companies, but prestige and a sense of duty and responsibility towards something larger and less immediate.

I've been a Kindle user since way back in 2010 with a Kindle 3G. I had a pretty huge amount of money invested into a library of books on Kindle. I installed koreader on my paperwhite earlier this year and haven't looked back. Even if it weren't for the limitations put on the walled garden for books in the kindle ecosystem, just the software upgrade alone feels great. When you hit buttons in koreader it actually responds in less than a second. I hadn't even realized how frustrating the UX of the kindle OS was until I realized the hardware was capable of feeling snappy.

There's obviously a lot you need to provide yourself that Amazon gives "for free" with the Kindle ecosystem, but using koreader with OPDS and kosync for synchronizing progress across devices, I'm very happy to be just buying DRM-free books elsewhere and hosting a small OPDS+kosync server on my home server. Installing tailscale on my kindle makes it so I can even fetch books/sync progress when I'm away from home without needing to expose my book server to the internet.

What extra features has over regular kindle software? I find kindle features enough but I want to know if I’m missing something

Not only is it the superior piece of software, the freedom it offers by dissociating the choice of hardware from the choice of software is another example why free software and interoperability is something we should strive for.

Funnily koreader comes with a lot of features that are useless to me, but I love that I can just disable the respective plugins.

I like the Readwise integration via plugin and the EPUB support, but for the first few days with it, I was busy understanding the menu hierarchy and trying to figure out how to match the styling and spacing of my native Kindle books. The out-of-the-box experience is unfortunately just "tasteless," and I needed some time to warm up to it.

Yeah and like the majority of open source software, the UI is garbage and unintuitive.

It shows reading stats that I absolutely love!!