Interesting use of a nested frame story—a story within a story within a story—all set within the Dark Tower series (as yet unfinished, by me).
It's difficult to miss the echoes of Life of Pi (2001), with its refutation of the "scorpion & the toad" myth, which is signaled there on the cover. Given King's overt remixing of Baum's Oz (1900), this seems unlikely a coincidence.
The author back-fits this novel into his already-completed Dark Tower series in much the way Sapkowski back-fit his Season of Storms into his already-completed Witcher series (both also graft themselves into Arthurian legend). Extending a completed story from the middle does not seem like something that would necessarily "work." And, yet …