I always feel like fictionalized histories of undocumented conversations should come with a warning on every page. A forceful reminder that this is all conjecture - possibly well-informed and intensively researched, but made up nonetheless.
I have the same trouble with films sometimes - like the film from Junger's A Perfect Storm. They never came home, so you don't really know who did what - the punk kid could have been the hero trying to save everybody or the skipper could have gone mad and jumped ship, you just don't know.
Anyway, if you have less difficulty suspending your disbelief, or simply enjoy a good story without worrying about whether it's accurate to the people the characters are based on, then you'll probably enjoy this.
The Kitchen Boy: A Novel of the Last Tsar is one of those fictionalized biographies that is a great story that may or may not be true - like a lot of fun books.
Note: It's easier to suspend your disbelief and enjoy the story if you read it with a glass of shiraz. I'm just sayin'