I think calling it a book for power users is highly optimistic. Much of it seems to be more like the manual ST should have had but never has, describing routine tools and pointing out keyboard shortcuts that you could find for yourself just exploring the default keyboard map. That is certainly a useful gap to fill, but there seems to be little if anything in the table of contents about real power user features like defining or customising languages, templates/snippets, themes, plugins, etc. I hope the choice of title doesn't lead to disappointment from actual power users while causing those who would enjoy and benefit from the book to go elsewhere.
I did notice that the sample chapter PDF has quite a few obvious layout problems, and that the expanded TOC on the web site has obvious typos, so the jury is out on editorial/production quality.
As a final comment, the author seems very keen on ST3, which makes me hesitant. I gave up and installed ST3 myself a little while ago, after too many packages I relied on self-updated into just not working any more on ST2. Now instead of a productive text editor that I enjoyed and recommended a year or two ago, I have a crash-prone, bug-ridden mess, which just has different packages I used to rely on that don't work reliably instead. So I'm pretty down on the whole fragmented ST ecosystem and lack of progress/support for existing customers right now. While I assume none of this is the author's fault, perhaps the timing of this book launch is unfortunate; it might be a better buy if and when ST3 and its package ecosystem are up to production quality, updated to reflect whatever the best available supporting packages are at that time.