It's basically what she said. It works for some people and not for others. But you could say the same of a ton of other drugs. The evidence isn't great and it often involves small sample sizes. That's why the only conclusion that you can draw is that it works for some people, which doesn't mean much. I wouldn't take it though. For a lot of these drugs the slim chance that it may work (and even when it does it doesn't 100% eliminate stuttering) isn't worth the possible addiction and/or side effects.