If a 'drink' has six shots, no wonder it is huge and costs 2-3x the price of a coffee. Not to mention the fat and sugar content if it is a dairy-based concoction.
These 'drinks' must be sustaining some of the international stores, especially where there is already a 'strong coffee culture', aka a competitive and well developed market for espresso-style coffees.
I believe there is a place for both, even though I am not a customer of SBs, because shopping malls (aka Westfield and a few others) tend to include a few if not most/all of the chains/franchises.
Then it's just a matter of whether the brand and the marketing is enough - or if the product makes customers loyal regulars.