I haven't read it, but from the reviews, it definitely isn't almost identical. The Rowlands biography is a book I like a lot, and it goes into a lot of detail about Bert's football. This book apparently doesn't have much on the football, and focuses more on Bert's times as a young man in Nazi Germany and a young man serving the German War effort.
Apparently, there's material in there which isn't especially flattering to Bert and a couple of high profile City fans (Sir Howard Davies and Simon Hattenstone) have given the book negative reviews. Davies reckoned that it contained a lot of information that, as someone who'd idolised Bert as a kid, he'd rather not have known. Hattenstone was upset that Bert's youthful enthusiasm for the Nazi cause was made clear but that no apology was offered for that.