How effective is using a mobile app to learn a language?

A well-designed app could reduce the amount of time needed to reach fluency.

Dedicated time spent using an app could give a more “dense” or “one-on-one” type learning experience. 

Encore!!! is designed to be used 3 hours daily without experiencing fatigue.

Many people listen to their favorite music playlist for several hours a day without getting tired.

Many of us listen to music when commuting, exercising, cooking, cleaning, etc. We end up not only enjoying the music, and being motivated by it, but we also memorizing song lyrics and melodies.