Yes, interesting stuff. I have read the Azrin, Nunn and Frantz study from 1979 which recognises that during their study it was conclusively shown that a deep breathing technique does affect a stammer. There will always be differing views, but the most powerful evidence that costal/diaphragmatic breathing works are the 1000's of people using it. Sure, it doesn't work for everyone, but after 35 years of misery I tried it and it's been life-changing. In the UK there are three organisations who train this technique, I prefer the charity Empowering Voices, and there are others worldwide.