Yes, it will. The Saver Day Pass also covers the routes serviced by Postauto post buses. You can find the Saver Day Pass validity map on the Saver Day Pass product site in the section Downloads.
Saver Day Pass – book earlier, travel cheaper | SBB
No, you do not need another travel card to purchase the Saver Day Pass. Simply make sure you are going to buy a full fare Saver Day Pass, the ticket sells from CHF 52.
As you are coming from another country to probably ride the Gelmer rollercoaster (quite a journey), keep in mind that the weather might not be your friend on the day of travel. Consequently, the SDP is not refundable in case of trip cancellation. Also, I do strongly recommend a reservation for the Gelmerbahn, it has become too popular in the last few years and long waiting queues have become a fact for those without a reservation.
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