If you ever take the hour long paid online test at the Enneagram Institute website, you will receive in-depth type descriptions of your potential types and instinctive variants. This book is a compilation of all those descriptions, which makes for a much better reference guide than the website.
The book provides 27 type descriptions (three instincts per type), where the health level is average or below average, and the fixation is pretty strong. So it is not that helpful in typing those who are healthier, though it does still include good info on how to continue to integrate and improve upon your personality issues.
I use this book mainly to type and understand others. I find that most people present themselves differently than they actually are, and it takes a lot of close observation and deep listening to discover the real person underneath. For myself, I utilize the last section of my type description, where Riso outlines common fallacies/traps to work out. They are spot on!
I reference this book regularly. A good book to keep on the shelf for therapists, advanced Enneagram enthusiasts, and parents trying to understand their teenagers.