There is much more to stuttering than confidence, for example for most of us signals from brain to mouth are not consistent or one area of the brain works more or less, there is not a complete balance like in healthy people. Of course confidence can help little bit, but is just for a while before something happens and everything goes back as it was. To really cure stuttering actual changes to brain must be done through specialized medicine or something similar. Really hope that more scientists work on this and find a permanent cure already. 1% of the worlds population is a big number of potential customers if money is what they care about.