Playing briefly, looks pretty good! -- though I wonder if there's a way to move away from using a source language (or maybe it does this in later lessons?). You really want to try to get your head 100% inside the target language as quickly as possible, and not be translating back and forth.
You can do this with the "free dialog" option from the beginning. The only issue with this is you do have to reference the actual lesson material to that point, so it's more of a review piece.
That said, my impression is getting to functional in a language quickly requires referencing a source language that is fully understandable by the user to build vocab and comprehension - ie. explaining a new concept in the target language using the target language for a B1 student is going to be inefficient and not expressive enough. Otherwise you're fortifying what you already know vs. actually building more knowledge. Things like comprehensible input are great but seemingly more indirect and less efficient.
If you have an option to get from zero to B2 fairly quickly, you are functional enough in the target language to use a myriad of options to fluency, including doing nothing other than conversing with others.
