Hi Sylvia, thanks for your question. Personally, I haven't had much success with Duolingo, and I've heard stories of people spending years completing the whole "tree" and still not being able to hold a basic conversation in the language.
However, since it's been a few years, I believe that Duolingo's Polish and other language courses have likely improved.
Regardless, I still encourage you to give it a try and see if it works for you. Remember, everyone learns differently, so what works for some may not work for others.