Look, I've had a serious stutter. I'm 18M and in Highschool. It got so bad to the point that I couldn't say my name. I tried your technique to. Yeah its good to build confidence and all but you're not getting to the root of your problem. Most times, it is your breath getting out of place, your vocal chords, facial muscles, tongue or lips getting stressed due to incorrect talking techniques. I would suggest a therapist. They really help with improving breathing control and other things, like pronounciation etc. I've been going to one, and it has ben going well.