KOReader: A free electronic-book reader for e-ink devices

I bought a Kobo Libra 2 quite recently, after an FBReader update on my ancient iPad rendered it useless. With out really even giving the built-in software a chance, I installed KOReader and tried to load an 18MB ePub containing every Wheel of Time book in a single file. It look it almost 3 minutes to open the file. Every rotation of the device took it another 3 minutes to re-flow the text.

Conversely, using the built-in software on the Kobo, the file opened in a few seconds. Device rotations were basically instant.

I don't know if I missed an obvious setting or if my ePub was fundamentally flawed in some fashion. For now, though, I'm sticking to the built-in software and just side loading files over the USB C port.