I think you just book the excursions you want (any price point) click on the SM pricing
You do not have to stick to the lower priced ones as with O life
once you use up the Excursion credit amount $800 pp in your case) the balance goes on your CC
Do they offer 25% discount with SM?
The website still shows O Life while people still have that option maybe that is where the 25% comes into play
It will be an interesting 2 yrs unless they make everyone take the SM at some future dye
JMO