I've been learning Russian for a year (currently at around B1-B2). None of these new age language learning apps are actually useful, even to get your feet wet. The old is still gold when it comes to language learning. You think you're learning with these apps, but in my experience you're not. They just don't seem to put anything in long term memory well. There is spaced repetition in some of them, but not enough repetition.

Good old audio course Pimsleur is better than all of them combined. Cortina Method is best resource to learn grammar and the book is so old it looks like a smudged typewriter print. All old methods are based on learning and repeating sentences after sentences rather than learning individual words. You really end up learning like a child. Pattern recognition is where it's at.

I can't recall anything I studied on Duolingo for Russian. I can't forget anything I learned on Pimsleur. And I finished the last module in January.