This book follows the form, if not format, of the Blue Rose Companion. In this case the book covers different campaign models. This includes Fantasy, Horror, Modern, and Sci-Fi. Each section includes various character paths, skill uses, feats, and powers.
Outside of the True20 mechanics, there is good advice for running the various genres and sub-genres presented. In particular, I enjoyed the Fantasy and Horror sections. The big surprise to me though was the Modern section. While I did enjoy the Modern d20 rules, I felt it really lacked something. Turns out it wasn't laking, it was over done. Thr True20 Modern is stripped down to just what you need and it is perfect. I lament not running more Modern True20 games with these rules to be honest. Of course, you can mix and match. I pretty much add Horror to everything so Horror-Fantasy, Modern-Horror and Sci-Fi-Horror are all things I do and they are all here.
What makes the PDF better than the print book is the ability to print just the sections you want. True20 is not 100% modular, like say GURPS, but it is pretty close.
If you have True20 and want more out of it, then this is the book you need.