Finished my Esperanto tree!
I just finished my Esperanto tree (also my first Duolingo tree) in 24 days, level 11, with 3704 XP, all gold! I'm so excited!
I know you're asking Cxarmina - but here's my perspective. The only way to get good and solid in Esperanto is through time and practice, and Duolingo is a good way to get plenty of both. Because of the nature of Esperanto (simple grammar) a traditional grammar based approach is still a good thing - although it's possible you've already had that if you've dabbled in Esperanto before. (I happen to know that Cxarmina had also "dabbled" before starting here.)
For sure, by the time you've finished the tree, you will be comfortable reading regular Esperanto texts with a dictionary at hand, and that's all the basis you need.