I tried Duolingo some months ago, to try Italian. After 5 days I lost my streak already and never returned.
Now I am thinking of picking up Spanish. I may follow your research, go with Duolingo until I reach the sweet spot and then use other resources. Now it is up to me to make it all the way to the sweet spot. Perhaps I will. Have someone I can converse in Spanish with, which should give me an extra push. Thanks for the extensive research and post on it.