Speech therapy is not effective all the time and will sometimes backfire but still more credible than certain mask or earplugs, or similar stuffs. Just bc speech therapy is not all the time effective and acutally its essence runs counter to the true way to curing stutter, thus speech therapy is now more and more dominated by cognitive/psychological therapies like self-acceptances, cuz most of PWS are mild PWS and after letting themselves loose from stutter, their stutter can be migitated by 90% counted by Minnesota University, so clearly more flexible than your so-called mask or something. One of my stuttering friends told me that at the beginning of the trial, indeed he felt his stutter migitated but after two weeks, he felt his stutter deteriorated cuz not only was he paying more attentions to his stutter but also he became addicted to that mask and his hearing was also migitated, so it was very counterproductive and misfiring. I swear to God that at present the most relible therapy is cognitive/psychological therapy, and the future treatment will be some physical therapies that can repair briain dysfunctions like TDCS, DBS, and etc., not random mask named after one man. We are not dancing with girls in a masquerade mate.Also, the root cause of speech therapies are not effective is that speech itself is an uncontrolled neurological process that is natural and unvoluntary but STs are always coaching you how to control your speeches which is running counter to the essence of speaking, so no wonder they will sometimes backfire. Think about it, speaking will force more than 150 muscles to work for it and this process is just natural, not in need of your conscious controlling, just like you don't contemplate which leg to use when walking, to which direction roll your eyes for looks and these processes are the like of speaking.