Learn Mandarin, properly
Most flashcard apps teach you to recognise words on a page. Funetical teaches you to understand them in speech. Reviews use varied example sentences, so you learn the language, not just the example.
Listening first
Understanding speech is the hardest skill, so it gets its own dedicated review track. Reading has one too, scheduled separately.
Varied sentence practice
Each word can appear in multiple example sentences. Reviews rotate through those contexts so you rely less on memorised clues and more on the word itself.
Spaced repetition
Reviews are scheduled at the right interval so you're not reviewing too early or wasting time on words you already know.