Not the commenter you're responding to but I recommend switching to your own custom set of cards using Anki after you've done the basics of Duo Lingo. I use Ank

Not the commenter you're responding to but I recommend switching to your own custom set of cards using Anki after you've done the basics of Duo Lingo. I use Anki Droid almost every day, and there's also an iOS, desktop and web version that all sync.