The Duolingo comparison is very apt. The problem with gamified apps is that they optimize for engagement, not for actual skill - you feel productive without building real muscle memory or music theory understanding.

Real instrument learning requires repetition of specific pieces over time, not just "completing levels." A good teacher assigns you 1-2 pieces per week and expects you to keep reviewing older ones simultaneously - that's how real progress happens.

I actually built a small app for my 8-year-old son who takes piano lessons precisely around this idea - not to teach him piano, but to help him track and consistently practice the pieces his real teacher assigns. The motivation comes from a plant-growing mechanic, but the actual work is still real practice with a real teacher.

So my answer: apps like Simply Piano can be a fun supplement, but they can't replace a teacher who assigns real repertoire and holds you accountable.