Collegeboard has officially released The Official Digital SAT Study Guide. Let me first come to the meat of this book which are the four practice tests. These tests are duplicates of the tests that are part of the free official Bluebook app available from College Board, the creators of the digital SAT. The four practice tests in the Bluebook app are adaptive, meaning the first section is identical for everyone, however the difficulty level of the second section(easy or hard) will depend on how well you performed in the first module. This is how the actual digital SAT will be administered. However, the tests in the official guide are not adaptive. Instead, what they have done is to include a lower difficulty second-stage module in the case of Practice Tests 1 and 3, whereas Practice Tests 2 and 4 include a higher difficulty second-stage module.
My recommendation is to just skip this guide and practice with the free official Bluebook app available for download from Collegeboard’s digital SAT site.
Apart from the practice tests, the guide does have overview chapters with brief summary of topics tested(Algebra, Advanced Math, etc) and practice questions. There are chapter drills that can be of value. In the past, collegeboard has released copies of these documents in pdf format to the public, however I have not seen those documents. Potentially this part of the offical guide could be of some limited value.