There is a fundamental duality that compromises Duolingo as a tool for learning: the ad revenue tied to the free version means that the goal is to encourage the user to move through the lesson as fast as possible to serve them more ads.
This past week, I was a part of some A/B test where I started with 4 hearts and had to watch an ad to get the 5th daily heart.
The paid version is fundamentally no different than the free version and I'd wager that the majority of their users are free so the design is then driven by this need to serve more ads to generate revenue.
There are so many little ways in which Duolingo could help users learn that are still within the design boundaries of the app, but would in turn result in serving less ads.
For example, I wish that I could see the definitions or play the sounds of all of the words on a given prompt where I have to select a word or match words after I've selected the correct answer, but that means I'd spend more time within the lesson. I wish it had a built-in word bank for review and not just within the game mechanic. It's awkward to leave the app, go to a browser, and have to look up words.
I increasingly see it as a mechanic designed around serving ads (nothing wrong with that; they deserve to get paid) but I wish that the platform would develop more features that evolve around helping people learn languages as well.
I think if the paid version had more utility for learning, I'd keep it around and pay for it.
