I read the book in VN and saw the movie at home. They are vastly different. Only the first half of the book is emphasized in the movie, before Rogers left for England. It was a happy-ending movie, guy-gets-girl, not so in the book. In the second half of the book, Rogers stole the girl from Townsend and married her. (probably fiction). Rogers moved to England to try to recover the personal money he spent arming his Rangers, failed at that, ended up in poverty in debtor's prison, somehow was awarded a commission to go back to America, and eventually fought against the Patriots in the Revolution. He was instrumental in the capture and execution of Nathan Hale. All of which is true.
The second half of the book portrays Rogers as a progressively negative character. It's a good book, far better than the movie. I don't know how much the author researched the facts, both positive and negative, Kenneth Roberts did, but for the most part, the book is pretty well supported by the facts. The facts don't say Rogers was a cad, later in life, but the book does.