While Richard's comment about the book might be true, I (private pilot currently doing instrument rating) found the book very interesting in the way that it introduces much of what I already knew (and much of what I didn't) from a completely new point of view. The thing is, pilots are confined in their own way of thinking, and fairly often know much less about the mathematical part of navigation than would be desirable. I personally felt my private pilot ground school was baby talk, the textbooks did not contain enough about mathematics, and it felt good to read something that assumes the reader went to at least high school.
That being said, the mathematics in the book are not scary, I felt the author intentionally did not use anything more complicated than high school math (mostly simple trigonometry), which he also said in the beginning of the book. My math was quite average in high school, and never really dealt with it anymore in university, and it still did not take too much effort to understand most of the book. It did require some brain work to follow the calculations, though. The most mathematical part of the book is the second chapter, "Vectors and Spheres", where I had to skip some of the calculations. The book could have used a little more explanation in this part, but I must admit, had I not been a little lazy, I could have looked up the necessary knowledge in a couple of days.
I am the kind of person who likes to ask a lot of "why?" questions in my head, and this book gave me answers to a number of them.
I imagine the book could be equally interesting for math students, as it gives meaning to the numbers - something I missed a lot in mathematics. While to me it was definitely the first half of the book that contained most of the new things, to them it might be the other way round.