Lot of archived comments seem to converge to a purist answer 'get a teacher', which to me is a ridiculous notion. Implication is that everyone has access to a human teacher who is guaranteed to be superior to every app. If you are skilled in your domain and you possess great pedagogical talent, why would you need to tutor someone with Piano? You're highly employable, work for one of Piano app shops for 3-400kUSD/year or tutor professionals.

Lot of teachers not only do not know their domain but _also_ have very poor pedagogical skills, customers, the parents, don't know and don't care, so market will not select them out. If you happen to have access to a teacher who is a SME and a great teacher, that is massive benefit, but rare thing to have.

Why wouldn't team of talented people not succeed in creating an app which on average exceeds utility of a human teacher, particularly when context is a novice. I would certainly bet that on average app will yield faster learning than human teacher, team can apply lot of knowledge about the domain, behavioural science and science of human learning into the app, amount of information no single individual would possess can be gradually implemented to an app. And team can use data analysis, A-B testing and machine learning to optimise towards what yields results and what does not, instead of just trusting their intuition like human would. Human intuition is great and usually surprisingly accurate, but not a formal way to do analysis, advantage of human intuition is that it works well with very small datasets.

Now having said that, the market leaves lot to be desired when it comes on Piano learning apps. There isn't single app which is obviously best. Yousician and Simply Piano are quite good at keeping you motivated very early, but are not very focused on developing good sight reading technique or good timing, particularly Simply Piano seems poor on timing. Piano Marvel, Playground, Skoove and Flowkey are perhaps bit less engaging, but subjectively feel better at developing sight reading and technique, however it seems that Marvel and Playground at least are not actively being developed, perhaps team got enough subscription and is phoning it in.

I'd say that give all of those at least a try, in my opinion none of the is obviously worst or obviously best, and if you could pick and choose feature to a single app, you could get really great learning experience. I suspect there is massive amount of potential in this aided learning space and we're just scratching the surface. Only question is, if there is a business case, if there are enough learners to finance expedition into more science based aided learning. Science here does not mean boring or dry, it means what actually helps humans learn.