Straightforward, to-the-point, and practical, this book is excellent in providing context and background for Bardon's books as well as hints to clear up some common misunderstandings. If Bardon is the "father" of this system of Hermetics, Rawn is like a helpful older brother who nudges you in the right direction, though he's always careful about making sure that you know you have to do the necessary work yourself. Still, I've found it very helpful to have a "guidebook" to Bardon's tomes that speak in friendlier and less archaic language.
All of Rawn's works are available free online at abardoncompanion.com.