I am sorry but I have to agree with this person too.
Booksmart has crashed several times on me as I work on this book. It is extremely frustrating. I am about to start trying to re-do a couple of hours work lost when I closed Booksmart. I notice there are a lot of .backup files but there seems to be no Help files on how to use them.
I notice there is an article "Back up, move, transfer or share your BookSmart books" but its dated 2013 so it may not be relevant to Bookwrite.
I recommend the following: backup each time you start working; save as you go; when you close the book File, Close book. When you finish working with the program File, Quit. Work slowly, do not try to rush BookSmart is is fragile.
Thumbs down to Blurb. We are not your beta testers.