Probably to sell more copies?
Oh, really? Another attempt to swindle hapless non-native teachers?
You must be joking, in general people are not that stupid when it comes to money.
The whole foundation of the book is the reader's own built-in perfect native pronunciation. The book explores this with many useful exercises to help you understand what your mouth is doing when it speaks sounds, words and sentences.
Interestingly, the author presents the course as a number of activities for learners to understand how they could master their pronunciation. I assume, it might work for native teachers as well.
What pronunciation should be considered 'perfect' is actually beside the point with so many varieties even within one country let alone certain personal characteristics, that is speaking about BrE solely.
This book helped me a lot and I'd highly recommend it (to native teachers). I think pronunciation is too often neglected, and yet it is so important in communication. Also, the study of pronunciation develops the ear, which will in turn greatly improve listening skills.
Absolutely. Broad generalisation hardly ever helps to get the real picture, still I'd rather go along with you on that - it could be fairly challenging, if ever possible, to teach what you have never been taught yourself.
Undeniably, the course is helpful for native teachers. What I am curious to know is why
only for native teachers.
IMO, regardless of anything, while speaking everyone is doing something with his mouth, lips, teeth or whatever he has to pronounce something meaningful. Why not use these activities to polish one's sounds?
On the other hand, if these activities can help learners start speaking English more naturally, why do you think non-native teachers cannot benefit from them as well?
Incidentally, A. Underhill is addressing a group of non-native teachers at the seminar and actually shows how a Spanish-speaking teacher gets her /ae/ right at last. Or, are we talking about different books?