Not relevant to the discussion but possibly for you: I discovered this 100% free no-signup audio-only course for Greek through a previous HN post. Amazing approach (like Michel Thomas but more charming and modern and free!):
https://www.languagetransfer.org/about
Of all the language apps I used Duolingo has by far been the least useful. I've spent hundreds of hours but took barely anything away (for FR, ES) If you must pay go to a proper app with structured learning, like babble or something language specific.