I’m a huge fan of this app for starting a new language. For clarity: this app publishes these courses in books and recordings; Mantano delivers that same content via this and the related apps. Assimil is a straight transcription of the book and recordings. The convenience and simplicity of doing it through Assimil would make it marginally better than the book+recordings format.
However, it only works maybe a third of the time the time. Most mornings, I get up, open Assimil , and watch the pinwheel-of-death spin for five minutes or so. Then I give up and get out the book and play the recordings from my phone while reading along. (Which is essentially all Assimil does.) This is really frustrating since the this app approach works best if you do one lesson per day religiously.
Bottom line: I feel like I paid for the course in Spanish twice - once through Mantano and once through a reputable online bookseller. I regret wasting the money at Mantano. However, if you really want to teach yourself a language, I can’t praise this app enough.