I think you're right: it is a knife at a gunfight, but I think it's within the context. At the bottom line, for behaviour change to occur, we have to change hearts and minds. With that comes the change in skill to counteract. We all like to believe that we are the masters of our own domain and we make decisions, but that's the issue: the decision-making does get clouded by all of these other things that happen. Life happens.
You're right, the app in and of itself is not going to do it. There's nothing magical about sitting in front of a computer or playing with an app that's going to make you do it. But if it can touch your heart, it can give you some knowledge, and it can help you keep track of it; that's the science that is shown to make a difference.