I did not follow Delferro. But I did some research about it. I know it is about you Middle rif breathing. An Opera singer did introduce the method. In Belgium we do not have the course but Netherland has a 5 day program. But also in this case it is all about the motivation to use the method in real life. And I surly believe that in the 5 day course you will learn to speak more fluently but the question is how much people will be fluent in the long run. How was your experience with Delferro. Did a quick diagonal reading on the pdf you send (will read it througly latter) and my first impression was that it is the same method you have in classic speech therapy. Do not use tricks or avoiding/synonyms. But analyze the stutter and be ok with it. I followed twice the classic therapy and it really helped me 0%. The focus is on your feelings and psychological.