*The app SuperMemo is often confused with Super-Memo
SuperMemo seems to advertise its courses and their efficacy by emphasizing the SuperMemo Method. The website states that it is the only scientifically-proven computer-aided learning method — however, the method is a typical Spaced Repetition System that Brainscape, Anki, Pleco, Skritter, SpanishDict, and countless other resources use. If SuperMemo made any special improvements, they do not stand out.
SuperMemo’s courses can be accessed through a monthly membership or through purchasing individual courses. Each course contains a series of flashcards with some interactive activities (such as fill-in-the-blanks, multiple-choice questions, and dropdown menus). In some beginner courses, like Hungarian and Dutch, you can learn basic pronunciation with the International Phonetic Alphabet; this can support you in both understanding and producing the sounds of the language later one. They also use native speaker pronunciation to train your ear.
The Fast Track courses may have potential, but there do not seem to be many grammar explanations, and it may be up to you to understand your errors. Additionally, you may find that you are suddenly reading translations from your target language in Polish, whether or not you speak Polish.
Overall, Supermemo seems okay, but there are probably other resources that will help you learn a language more effectively.