I find The Buzzing Book to be a very good and helpful book and i have used it for a number of years now. James Thompson is obviously a intelligent man and a good teacher. Especially i find the things that are written in the book to be almost more interesting and helpful than the actual exercises... almost..
If you do the exercises right the buzzing book can be very helpful. Personally the book have helped me with: Intonation, articulation, air use and air feel. I recommend that you read through and pick out the exercises that work for you.