Promo on 3 Day Swiss Flexi Pass

Hi DJ, and welcome to the forum! As for the 3 day Swiss Saver Flexi Pass: it's best to fill out your country Canada and other travel details under the header 'Where to purchase your Swiss Flexi Pass' at the Swiss Flexi Pass page. You'll then get to see an up to date overview of purchase options and prices. As you can see, it would be cheaper just to order your pass through RailEurope and have it shipped to your home address by mail, rather than using the current offer from STC or buying the passes locally.

I'm afraid you haven't quite understood the Swiss Flexi Pass: it offers a number of free travel days, but only remains valid up to the last travel day. Right after the last free travel day, the pass is no longer valid and doens't offer a 50% discount anymore. The 50% discount only applies to all days in between the first and last day of the pass. These and other specifics are mentioned at the Swiss Flexi Pass page, under the header 'Swiss Flexi Pass features'. In your case, this means that you should use the 3 free travel days for 1) the transfer Geneva-Spiez, 2) on of the days in Spiez, on which you want to make the longest and most expensive trip and 3) the transfer Spiez-Swiss/German border (probably Basel). On the remaining day in Spiez, on which you want to make the shorter and less expensive trip, you'd use the 50% discount.

If you like the idea of free traveling on all 4 days of your stay, consider the 4 day Swiss Saver Pass. Prices can be checked as explained above. It's only a bit more expensive than the Swiss Saver Flexi Pass, but offers free traveling on all days of your stay. So you don't have to buy reduced tickets on one of the days in Spiez, and if you want to make trips from Spiez on both days, the 4 day Swiss Saver Pass will most probably turn out to be cheaper than the 3 day Swiss Saver Flexi Pass.

You don't have to book mountain excursions in advance. You can just show your pass at the valley station, buy a discounted ticket and get on board. If you don't book in advance, you can indeed change plans according to weather circumstances.