[yakireev]

Try their desktop browser version. All the ads can be blocked by uBlock Origin, there are no limits on what you can do whatsoever (I have no idea what are these "hearts" you're talking about), and most importantly - you can switch to the "write your answers on a keyboard" mode.

That last bit makes a hell of a difference. One thing is to click through, another is to actually translate a sentence or to write it down in "type what you hear" exercises, with hints showing up only when you explicitly ask for them. It makes the whole thing harder, but is absolutely worth the effort. You'll pound not just the words into your head, but also the grammar.

I learned two foreign languages in the recent years (as in: can read a newspaper or talk about my last vacation, humble brag!), and Duo was one of the keys to success (Anki & having an actual teacher were another ones). I believe it wouldn't work so well if I was just "clicking through" on mobile.