As an expat for over ten years I say dont let the "employee's jovial hollers" scare you off, that enthusiasm is just some good ol' American over the top attitude.
Jamba is the real deal when it comes to smoothies. California is a place where smoothies are almost as sacred as tacos- so I am happy to have them here to replace bad knock-offs (sorry jugo and booster...you just really can not compare)
Medium is called "original" because for years that was the only size offered. Like In and Out Burger, Jamba focused on one quality product before introducing more options.
If its your first time here forget the fancy concoctions. Try something simple from their first menu like Strawberries Wild or Razzmatazz. Enjoy!