TL; DR: This book doesn't describe character arc in a way K.M. Weiland's book does and I didn't agree with everything the author claimed, however, I did find some useful new tips in this book that I will definitely be incorporating in my own writing. Definitely recommend.
First of all, this book needs a line editor. I'm not one to complain about one or two typo's, but for a book of this price point I don't expect to spot as many typo's as I did. Sean Beam, anyone? There aren't as many as for the text to become unreadable, but they were enough to notice and for me to make a mention of it.
One of the things where I found this book lacking was the area between what the character wants and what they need. The way Jarvis explains this, it's like they're the one and the same and it often isn't. It touches on it briefly here and there, so I wouldn't say it isn't there at all, but it's all very much on the surface.
There was also a bit about Hamlet where she claims that killing Claudius isn't Hamlet's goal, it is avenging his father. This didn't make sense since earlier she claimed that a goal needed to be tangible and avenging his father's death can take one many forms, so the qualifier of killing Claudius would be needed to determine whether or not the goal has succeeded. To be fair, i haven't read Hamlet, so I wouldn't know if any of this is true, but to me the goal of 'avenging something/someone' needs a qualifier of how the avenging is going to take place for the above mentioned reasons.
The Rising Action was also a bit fuzzy, but the excellent explanation of Crisis, Climax and Dramatic Question more than makes up for it. Part 3 was also extremely useful when it came to the Dramatic Curve for ensemble characters and provided me with some new insights.
All in all, I think this is a great addition to any writer's tool box. It reads easy enough and the way the material is explained is engaging. I finished this in about two days and made tons of notes. Definitely recommend.