I’d say it’s definitely not worth it to try Rosetta Stone. It’s expensive and too slow when there are better methods. It’s flawed since it doesn’t use the advantage we all have of already knowing one language.

I don’t use many apps that work for multiple languages (I prefer language-specific ones), but here are a few that I find great: Polygloss, Anki, HiNative, and Tandem/HelloTalk. I suppose there are Polish-oriented apps but I haven’t learned this language (yet?) so I’d say you should try a few ones and see how you like them.

You could also try Memrise as a support. I’m not a big fan, but I know many people who have used it as a great bonus for their studies.

Hope that helps!