I've used KOReader in the past, and it's awesome! Keeping the jailbreak when my kindle randomly decides to updates itself, not so much. (yes I followed instructions to disable updates, but it still somehow managed to update) At some point it becomes too much of a hassle.
Though OP has his kindle offline all the time, so not a issue for them.
It's gotten a lot better since we entered the KindleBreak era. The community went nuclear, and now instead of applying various hacks to try and prevent updates from being downloaded, the jailbreak package includes a little service that (as I understand it) watches the disk and immediately deletes anything that looks like an update package. The MobileRead "Open Sesame!" thread [0] has all the modern tooling in one place, if you're interested.
Though OP has his kindle offline all the time, so not a issue for them.