I didn't find it useful for me, app just explains all the same stuff that I've heard dozens of times on YouTube and I think it's just the wrong approach. Basically the app explains "what it means", but the problem for people like me is not understanding "when and why to use it" in some real-world problems, not super simplified a+b examples. It's like ok, I learned it, what's next?
Since I'm in the process of learning English, I'll make an analogy like this. So this app is just like a dictionary with translations, it has all the words and terms, it says what they mean, there are even 1 or 2 sentences with examples of use, and technically you can just memorize all words, but that won't give you the ability to speak English, at most now you can just understand the text and some parts of what people are saying, and even that will have limitations, because you don't know the context, and you can't create sentences yourself, aka like in programming when you can read someone else's code (some times), but you can't write it yourself. In order to actually learn English, you need to not just have a memorized vocabulary, you need to see and hear how people actually use words, and only then try to use them yourself, so process goes like this: learned a word -> listened to how it is used -> try to use it yourself. The problem with programming is that you simply have no way of seeing how people using those words, even if you try to read someone else's code, you still won't have the context with which it was written, so you skip this middle part, because you have no way of getting it, so you go straight to the third part, and the problem here is that there is no feedback, you are simply forced to put this puzzle together blindly, basically brute forcing your way
Regarding to the app itself, I also think that it oversimplifies everything too much, so that starting from lesson 15, the code in the examples and practicals simply ceases to make any sense at all