The second Jeonjijeok Dokja Sijeom novel is a notable step down from the prequel. The pacing is far, far too frantic, the plot developments are pretty random, and the character actions are simplistic. I see no reason to go any further.
I had been wondering how there could possibly be a continuation of Dare ga Yuusha o Koroshita ka considering the way it ended, and the second novel being mostly a prequel turned out to be the answer. Focused on someone with a tangential relationship to the hero, this story hits many of the same beats while giving a bit of a wider view of what was happening in the world before the demon king fell. And while not quite as good as that first novel, it works well as a supplement.