I teach English for a living, but suddenly find myself needing language instruction as well. I think this app is very powerful, but if you are serious about studying -- you will also need to find other resources to help you along the way. What is most lacking -- at least from my perspective -- is the formal component of study: e.g. grammar charts.
Dont get me wrong, I think you can get pretty far with this apps presentation style -- but for the language to really click I think tables are necessary.
Also, I strongly recommend using Quizlet (another app/website) to create your own set of review cards.
Good luck!!
Prof-come-student about Babbel – Learn Portuguese, v4.3