My friend did it, his stammer is very severe. It worked for a little while but he's back to the way he normally speaks now (didn't keep up with the techniques). I think if you want to do the McGuire Programme you need to be ready to work hard because you are fundamentally changing the way you speak. You have to use coastal breathing with every word you say, people do say its easier as time goes on, but it takes daily work. Some people do have great success with it though. If you're up for it, go for it. Especially if your stammer is less severe. I hope I haven't put you off lol. (But it worked for my friend until he stopped using the techniques and like I said, he has a severe stammer so it did technically 'work' for him.