FYI, it has to be an actual Starbucks. If it is CAFE PROMENADE and they use Starbucks product the card is still good.
Also, even if the card is only good for single expresso shot beverages it can still save money if you drink Cappuccinos or Lattes. Also, the card is shareable.
Depending on what else you drink, it might make sense to buy the refreshment package