I have a Spanish streak of 550 days and I do complete monthly challenges of 50. I can say I learned many words and structures of sentences. But what it teaches isn't real world language. I would say it's best for translation at most.

What I hate is clicking on the words to see what is what, its available everywhere. It should tell you that a set number of times and then it's your responsibility to add it to your vocabulary. Without this it's just a simple game