It's very useful for practicing purposes, but if you use it as a "cure my stuttering" device you will be disappointed. Your brain gets used to its effect after like 30 minutes. The best way to use it is to practice with it. It's great and helping you slow your rate and promotes monotone, prolonged pronunciations. Again, it's a very useful device to PRACTICE with. It's NOT supposed to be a device that cures your stuttering during a conversation or presentation. Source; have used and owned a DAF machine or app for 10 years.