If your version of Dawn of Wonder has 66 chapters, you have the third edition, and you don’t need to read this. If you are one of the first 15 000 (or thereabouts) readers whose versions have only 62 chapters, you are missing this addition which has some important elements that will reappear in the sequels.
If you haven’t read the book, you probably shouldn’t read this, which likely makes the prospect irresistible. The free sample of Dawn of Wonder is around 70 pages, but if you are someone who likes to sample the middle of a book before making a decision, you are welcome to jump in here. The spoiler-index of these chapters is relatively low.