It is good for the script and early vocabulary, and it will not make you able to speak. Duolingo's Hindi course is smaller than its Spanish or French courses and stops well short of conversational level — treat it as a first month, not a plan.
What it does well
Devanagari. Genuinely one of the better free ways to learn
the script, with plenty of repetition.
Daily habit. The streak works. That is not a small thing —
consistency beats intensity in language learning.
Free. No argument there.
Where it stops
The Hindi tree is short. Finishing it leaves you somewhere
around beginner-to-lower-intermediate, not conversational.
It cannot hear you. You can complete the whole course
pronouncing त and ट identically and never be told. Those are different letters
and swapping them changes words.
Odd sentences. You will learn to say things you will never
need, which feels like progress and is not.
No gender correction. It teaches that a man says
karta and a woman karti, then never notices when you get it
wrong in the wild.
The honest verdict
Use it for month one to get the script and a few hundred words. Then add
something that talks back. Learners who stay on Duolingo alone for a year
almost always end up in the same place: they can read a bit, understand a
little, and cannot hold a conversation.
What to add
Listening to real speech daily, and one weekly session with a person who
corrects you. That combination is what converts recognition into speech.
Our guides are free, and lessons
start at $6.
Practise this with a teacher
Reading an answer is one thing; being corrected while you say it is
another. EkGuru tutors teach one to one from
$6
a lesson, and most offer a trial.