First off, this is either a graduate book or a senior undergraduate book in Physics. The book assumes at least 2 years of college math, preferably for engineering or physics folks.
What sets this book apart is the focus on physics is perfect as we understand E&M theory at this point. Unlike other imperfect college texts like Lorraine and Courson, this book contains no errors. While some may no like "and the proof is left to the reader", the book is meant to teach people who are focused on physics but can describe the process mathematically as well as in regular language.
The assumption is that there has already been a rigorous introduction of both physics and mathematics so this book is NOT a casual read.
The beauty of this book is that it's not just teaching knowledge but it teaches one how to think. To those who can rise to the occasion and draw upon their education, professors and peers, there is the satisfaction of really understanding E&M clearly and concisely.
To those who only seek rote knowledge, this book will be too challenging.