This book was written back when there was an East and a West Germany, something that is mentioned a few times. Also, it was written when Prussia was still remembered by many people, being if not exactly a live issue, but one with some residual currency.
Time has moved on. Another 35 years or more has passed since this was written and the book now feels incredibly dated. This is in both content and writing style. Thadden seems to almost skirt around points and uses a lot of words to say very little.
He deals with themes, rather than history. If you wanted to know what the burning issues were in any particular period, you'd come away from this book non-the-wiser. In fact, for anyone who hasn't already read a few books on Prussia, this book would probably convince you that you have no need to read any further.
It might be useful for the odd student who wishes to bulk out their bibliography, but I doubt anyone else can't do any better for a book on this topic. I got half way through before I realised it wasn't going to get any better. I resent the day or so I spent reading it.