As an opera singer who has been training for over 12 years in overseas and back home. I have never met any teachers or collegues that don't know about this book. This book has more or less become our vocal "Bible", suitable not only for the advanced classical singers, but perhaps even more suitable for the beginners. Despite the fact that similar editions from other publishers of these songs are readily available, I still think this edition reigns supreme.
The songs chosen in this book, in various levels of difficulty, are great as teaching materials, as well as performance materials for recitals and exams, etc. In my teaching experience, I find that every singer finds something in these songs that can improve their singing voice, maybe because I think it teaches them so much about the rudiment of legato(smooth) singing.
For anyone wishing to take singing lessons, particularly that of Classical singing, this book is a MUST-HAVE in their music library! I will be very surprised if a Classical singing teacher do not ever use or recommend this book for lessons at some stage. Learn all the songs (at your own pace) and you won't be sorry that you did :-) VIVA LA MUSICA!