This is an actual GUI. They're two very different beasts, with two very different set of capabilities, aimed at two very different set of use-cases. The fact that you happen to be able to launch KOReader with both is basically a happy coincidence

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In the very narrow (for KSM) context of KOReader *only*, I tried to summarize this
in the KO Wiki.
But that's very much in the specific context of KOReader.
TL;DR: The choice is yours, and choice is good

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