I don't remember frankly, maybe something with the script, maybe something with KFMon. Lack of integration with the Kobo OS itself? Maybe it had to be rooted to install KFMon, but I was reading Koreader could just run inside nickel menu maybe? But yet the script installed KFMon?
Again, I don't remember. And whatever it was it's not worth me trying to reinstall it just to remember what it was, and then to uninstall it again.
The Kobo OS is good enough for me to recommend it to family, there's nothing wrong with the iPod experience of uploading books.
But Koreader+Tailscale+Kavita OPDS is the best reading experience I've ever had.