What it clearly demonstrates to me is an author/historian being intellectually honest and following his research instead of any inherent bias. Roberts is clearly at home with his subject and he is also a scholar and a gentleman. I interviewed him by email some years ago for another site and was impressed with him as an honest man.
The book is taking some flak from the 'usual suspects' on Amazon UK because the book is sympathetic to Napoleon. All it adds up to is faux outrage and sour grapes.
Good for Roberts.