I found this book just by chance and really believe that it's a treasure.
I got it for a student of mine who hates math. He's 12 years old, just like Robert in the story, really active, more interested in any computer game than anything having to have to do with school, generally doesn't understand a lot of mathematical concepts nor the need to study math.
We have begun to read the book together, chapter by chapter, each of us taking one of the parts - sometimes he's the devil and sometimes he's Robert, depending on the mood he's in. We have a lot of fun making up voices for the two characters, and he really pays attention and tries to follow the math concepts. We have a lot of fun screaming out the dialogue and bringing the scenes to life.
He's also fascinated by the illustrations which are captivating and original.
This boy, who would rather play soccer or video games than have anything to do with his studies, now asks to read the book, and is a bit more patient with his homework. I can't tell you what that means as a teacher - to have found something that works so well with a student. The original approach to basic math concepts is also a gem and he's being introduced to sophisticated math skills in a very nonchalant manner.
I strongly recommend trying the book and seeing if your child reacts well to it as well.