Mansfield was only ever really in two films of note but has managed to carve out her own niche in Hollywood - due to a combination of things: those two films were for auterist darling Frank Tashlin, her big boobs, her massive IQ, her famous daughter, her interesting death.
Strait did press for Mansfield for a number of years so had inside knowledge. I had this image of her as a super smart girl who could play the fiddle and was better than what Hollywood had to offer. This confirms that but also shows her to be a bit of, well, fool - she was hooked on booze, and sex, and men, and fame, and constantly made bad decisions. Her ambition and work ethic got her to a decent position in Hollywood but she blew it with bad choices, particularly with management, projects and men.
She loved boozing, and sex, and being famous. She wasn't a particularly good mother, or actor. She worked hard enough to keep her profile going - when the film roles dried up (relatively quickly) she kept things going with live appearances.
If you're interested in Mansfield's private life this really is a warts and all - there are a lot of warts. Mansfield doesn't come across as a terribly likeable person. There are some interesting bits, like the fact she shaved her pubic hair (it's that much of an inside job!) but mostly it's harrowing, with a lot of squabbling and failure. Her death almost comes as a relief.
I would have liked to have read more about the films but that wasn't the focus of the book. (There is a lot on Promises, Promises and Single Room Unfurnished.) It wasn't a fun read.