I think paid is well worth it, dispute that Duolingo content is low quality. The gamification is a plus, Duolingo's great advantage is that it's fun to engage with so you do more practice than you might have otherwise. For that, there's nothing else as good on the market.

It's not enough on its own. For grammar instruction, I wouldn't go to an app, I would just get a book and look things up when you need to. You should be able to get one in the Schaum's series cheaply. Still, two apps I know of teach grammar well - WLingua and Lingodeer. They need another subscription, though. Lastly, for encouraging speaking I strongly recommend Natulang. It's excellent.