Dulingo - Opinion From A Top 5 % Of Learners
Duolingo is one of the most well known language learning apps. Duolingo has 500 million users worldwide. They have 103 language courses in 40 languages. They have a number of language courses in minority and endangered languages.
I downloaded Duolingo in February 2019 and use it mainly as a supplement to other language learning methods. But, I have used it as the sole resource for some minority languages like Navajo.

Despite having completed the tree 🌳 for Navajo my knowledge of that language is still extremely limited. I do not believe many people would be successful in learning a language by just using Duolingo.
Duolingo can be a valuable resource for language learning if it is used alongside traditional methods and exposure to the target language. With the Internet and streaming services it is now very easy to be exposed to different languages regardless of one's location.
I have and still practice over 15 languages on Duolingo and strongly believe the time spent is far more valuable than wasting time on Facebook or watching a programme/film in a language/s that I already know.
I did not think that I spent much time on Duolingo and was very surprised when I was notified of my learning stats on Duolingo. According to Duolingo I spent the total of 2494 minutes 41.56 hours on Duolingo and I am one of the top 5% of learners on Duolingo. On average 3.46 hours a month which is less time ⏲ than I spend in a week or somedays actively studying a language.

I only use the app occasionally because I prefer their website. They do have a premium option but, I have not used it and doubt I will.
Learning any language including your own takes thousands of hours of active study and even more hours of language exposure to that language.
A monolingual five year old child will have been exposed to their first language for their entire life and slightly more if you consider language exposure from before they were born. Even to reach the same language ability of a young child is quite an achievement.
One of the most effective ways to learn a language is by living in a country/area where that language is spoken but, that is not always possible. The next best thing is to surround yourself with that language via the Internet, radio 📻 and television 📺 and by actively speaking the target language with a native speaker.
I have found Preply to be a great resource for actively practicing languages with native speakers very cheaply with lessons available for as little as €2 an hour. If you use my link above you will receive a significant reduction with your first lesson. It is worth considering that tutors on preply do not get paid for the first lesson 🤔 therefore it makes sense to choose a tutor that is within your budget and one you believe will be suitable.