Hello Xinneennach56
The Swiss Half Fare Card is the tourist equivalent of the Half Fare Card; thus, yes, it can be used for the Duo Day Pass, too.
The Duo Day Pass is a simple day pass.
The Swiss Travel Pass grants the same amenities as a day pass
- plus, it includes the museum pass (free admission to 500 museums),
- plus, it grants some discount for mountain railway tickets what a simple day pass does not unless both travellers hold the Swiss Half Fare Card,
- plus, it comes with the Swiss Family Card; with it, children can travel for free while being accompanied by their parents with a valid ticket.
Kind regards,
Roland