The book contains course notes and quizzes to be taken while watching the videos. There is a decent amount that is flat out not in other sources or is not highlighted despite being high yield. Most of the people I talk to about DIT tell me that you will get 5-15 questions correct based on information that is not in FA but is covered in DIT. Presumably that material is in the book or is present after you fill in the quizzes. Comparing it to Goljan is not very helpful since it focuses on path and is not a comprehensive review like DIT is designed to be.
I know some students who have shared a DIT subscription and only had one book between them and it worked out. I also know people who have forgone taking notes into the DIT book and just used FA for notes and the DIT book for the quizzes. Everyone tells me that actually taking the quizzes and filling in notes is crucial to getting everything out of DIT. But if you're not going to watch the lectures then getting the book is probably not worth it.
