TL;DR you have to be like Duolingo only if you plan to monetize like them.

---

I think it totally depends on your goals, let's try breaking down why Duolingo is doing what they're doing, and then we'll try to map it onto your own goals.

So, Duolingo monetises via mostly subscriptions, this means that their sales funnel is something like UA channels -> conversion to install -> conversion to subscription -> conversion to renewal.

Leaving out the first two steps (it's marketing I am not competent enough to discuss them), we arrive at "conversion to subscription". The only thing I'll mention regarding user acquisition is that we have to keep in mind, that users from standard marketing channels are always less motivated/interested in a product, that organic users, who are actively seeking the solution for their so called "pains".

In order to convert a user to a subscriber, one has to have an appealing value proposition, which for Duolingo is something like "learn the language in a really fun and engaging way", they support this proposition by including gamification elements, both mechanical (streaks, lives, mini-games) and narrative (cast of characters).

The perceived value for a user also becomes more apparent the more the user interacts with an app (see metrics like time spent, retention rate, stickiness). Thus, the aforementioned gamification mechanics also serve retention purposes (namely, the main thing - the streak) both between sessions and inside a single session.

So the more a user is with Duolingo, the more value she perceives in it ("sunken cost" fallacy also comes into play here), and the more the probability she will subscribe.

---

Now, coming back to your question. From your post I see that you're talking about "today's market" so I assume you want to sell it somehow.

You face a choice:

- Go standard UA route, acquiring users via ads, this will potentially get you a lot of traffic, if you have money to spend. Downside: you have to have A LOT of money to spend in order to make positive ROI, as ad traffic is not as motivated, and you'll have hard time making these people convert to paid users without all that fluff Duolingo is doing. Sure "calm tech" is sort of popular thing nowadays, you can play off of that, but still, you have to convince these people to stay with you, learn the value of your thing and eventually pay for it.

– Target a niche in a non-traditional way, via Reddit (though it is not that non-traditional way nowadays), communities etc. Basically direct sales. This way might get you much more focused audience who will gladly be your paying customers. Those people will NOT need bells and whistles. Downside: you really have to nail the solution for them, or they'll get back to their custom Anki decks.