Mike Hagen takes the guesswork out of navigating the users' manual that comes with your flash and trying to apply experience and intuition to using any of the line of Nikon Sb flashes. I bought a couple of them after seeing how versatile and powerful, for their size, they demonstrated in a Nikon video. I have some experience with flashes, beginning with the old days of the guide number system where you applied a formula with the variable of flash- to- subject distance to get a good ballpark exposure (this formula was applicable for the old style flashbulbs as well as with the early "speed lights") and ranging up through the D-TTL flashes. However, I knew that I didn't quite completely understand what all of the buttons did on my Sb-700's, and Mike Hagen, the outstanding photo guru, provided the answers.
This book covers all of the issues of using flash, from a basic, thorough primer on flash theory to specific functionality of each of the current, and recent, Nikon iTTL flashes. Unless you're expert in the use of your Nikon flashes and pretty satisfied that you are proficient enough to show the less initiated how to use the devices, I'd recommend this book. Event the basic stuff you probably know is worth reviewing in the context of using the Nikon system.
It may not be apparent to all photographers how much factors such as white balance, flash power and synch mode affect the finished picture, but Hagen describes these concepts and more clearly. He puts all of the knowledge he has to offer into a coherent 5-Step Plan for ensuring that nothing of importance is overlooked when setting up a shot. Everything comes together nicely in the final section of case studies of flash photographs where the author reverse engineers the shots to make the techniques in the book more understandable.
This is a thoroughly enjoyable book which answers more questions than you may think you have. I liked reading it in eReader form because the book will always be available for easy reference instead of being tucked away on a bookcase. It's highly recommended by me in any form you like to read it.