Is an app appropriate for this? Have you looked into speech therapists? It sounds like you need a professional who is trained for this sort of thing. Not everything can be handed off to an app.
Oh, yes, he has therapy - but therapist can't do everything either - a lot of reinforcement has to happen at home. Also, is been known that using apps like this (in addition to the therapy) can make a difference in when they learn to talk. It also gives them a voice while speaking is under development, and that in turn presents a lot more interaction and learning. The app would be just one of the tools in use though.
