In Duolingo I have grammar and short stories, which I can follow and built my grammar and vocabulary. Drops is different that is why I use both. It is a pity that in the free version of Drops I can’t do more than 1 language at once.
In Duolingo I can go on with learning till I make to many mistakes. In Drops I only have 5 minutes and sometimes some bonus seconds. Besides that Drops is categorized by theme. This means that I can learn all fruits together, which is very handy when buying fruits on the local market on the road.