The book appears to me to be the contents of use-the-index-luke.com. My friends impulsed bought it when I told him I was planning on buying it after confirming that it had more content than the website but after skimming the table of contents it doesn't appear to have anything more than the website.

Still, its good to support Markus' effort and if you prefer having a PDF rather than going to the website, just buy it. It's like $15.