Yeah, that's a big statement, but considering the fact that I own 7 other major propulsion books and refer to this one 10 times more than any of the others, I think it's definitely true. All of the top Aerospace Engineering schools use it, and for good reason.
It is NOT a teach-yourself book. If that is what you are into, then go buy something with more pretty pictures, because some sections take some work to dig into. But if you are Senior level or grad student, then the book will be very good for you. The content in the book is very insightful, and if you go through the book concurrently with a course it is a great help.