Yes - I do think the app can help you with bad habits you've
picked up in English.
That said, it's important to know ahead of time what the path ahead of you
looks like, so that you don't get discouraged. Once you have ingrained bad
habits, you don't really get *rid* of them; you build new, good habits
*next* to them and start using those new habits often enough that they
become more and more comfortable for you to use.
So with pronunciation, you will have the ability to speak English with an
Italian accent. As you use the app, your ears will get better at
recognizing what a good accent sounds like, and you should find it easier
to make an American accent. At first, that American accent may feel a
little fake or silly, like you're pretending to be some American actor. But
the more you use it, the more natural it will become, until you use it more
often than your Italian accent.
On the grammar/vocab front, if you have a habit of translating, that should
naturally fall away in time, as you do a lot of exercises where you're
memorizing English words *in English*. Those kind of immersive tests will
push you in the direction of thinking in your target language. One hint, in
terms of strategy: don't spend a lot of time making flashcards for words
and parts of grammar that you know already, even if you only know them in
translation. Instead, focus on new words and new bits of grammar. You'll
progress faster, and the old words will show up in those sentences anyways.
Best of luck!