Looking at the authors, this book would be more about security, rather than reliability.
(disclaimer: I work at Google)
Disclaimer: I work for Google
The first book is a solid overview of how Google does SRE and outlining each of the various concepts (error budgets, blameless culture, etc..). The second is more of a practical guide on deploying SRE into an organisation, a lessons learned type of book.
(I work for Google but not SRE, just enjoyed reading the books)