I watched the channel 4 program on the McGuire method and it was good but limited information due to editing.
I wonder what the follow up is and if it is just to encourage and coach breath techniques. If it works for you that is excellent and keep it up.
If you can control stammering by behaviour then it supports my view. I would do it a different way.
If anyone is interested in a workshop for a day let me know and I will see what I can do.