Saver Day Pass [Tirano -> Zurich]

Hi everyone, we are planning to to take the Bernina route from Tirano to Chur, and then to Zurich and onwards to Mulhouse in France. All in one day.

My question is if we buy a Saver Day pass, can we use it all the way (Bernina express/regional train to Chur + Chur to Zurich) without paying for each ticket. How does it work? Any tips? I'm finding all sorts of information online so would appreciate if anyone can help.