Language-Learning Apps

A few weeks ago, I referred to one language app, and now I’ve been told about another, the “Vocabulary Trainer”. It’s a “a mobile app to learn the most frequent words, travel phrases and slang (in total over 10,000 words and phrases) in over 30 languages.” It sounds intriguing, but I’m not sure if I think apps are the best way to learn languages. They can help in the moment, but I wonder if the material actually stays with you. What do you think?