This book is a very great book in my opinion except one thing: the signature of the metric. It would be excellent if the text uses the (-+++) signature instead of (+---) signature. The reason is because this book is at the introductory level above Schutz's First Course in GR but below Carroll or Wald's GR texts, thus signature difference is at best confusing. When the practitioner is more expert in the field (e.g. used to working in spinors etc. with different signatures for simplicity), this signature convention does not matter.
This book's main selling point is explicit computation, including explicitly showing all the G and c (which are set to 1 in most texts for clarity). Therefore this book is extremely useful for checking calculations and verify understanding. In fact, this text is about more than 50% thicker than Schutz with almost the same "main points" (except that here they expound more on variational principles and Reissner-Nordstrom/Kerr geometry) because all calculations are done explicitly. The chapter on experimental tests and calculations of trajectories are valuable. Most importantly, the chapter on linearized gravity is done explicitly and this is extremely useful, as to my knowledge many (if not most) texts do not treat these things as clearly as here (especially explaining the use of Green's function!).
In this sense, this book can actually not be read as "learning source": one could go from Schutz, then Carroll or Weinberg or Wald directly while using this as intermediate "check-and-balance".