Hey I'm a speech-language pathology assistant, who also happens to have a stutter, and I've looked into quite a few apps similar to speakeasy as well as the science behind it. The speakeasy, as well as apps similar to it, work because of something called the choral effect. Our brain has mirror neurons that are activated when we mirror the speech of another person, these neurons aren't typically effected by stuttering. In my own person testing, even cheap audio delay apps can achieve the choral effect but it isn't a permanent solution to stuttering. (I just used a free app called 'speech jammer' on the apple app store). Unfortunately, the potency of the choral effect wares off over time as your brain gets used to it (it's pretty smart after all) and your fluency will decrease again. That's not to say that utilizing the choral effect isn't a useful tool for us but it is just a tool. I hope this helped! I'm by no means an authority on this subject but this is just what I've come across in my personal journey. Good luck!