So, I had speech therapy when I was a kid, from 8-11 years old. At the time, I didn't really get it, or even why I was doing it. However, with hindsight, I use a lot of the tools that I learned back then, today (I'm late 30s now). Whether or not it's effective depends on the therapist, the methods, and also your mindset going into it. Most importantly, it also depends on what success looks like to you. All of those factors will determine what you get out of it. A big piece of it (at least when I was doing it), was how to approach words and sounds that cause us trouble (very useful indeed). I've found that there's a certain percentage of my stutter that I know will always, always exist, but I can control the rest of it to the best of my abilities by using certain techniques and by continuing to identify and control anxiety that aggravates the stutter.