This is an excellent opportunity to practice grass roots skepticism. Ask yourself: By what mechanism is this supposed to work? How does the proposed mechanism align with what we know about science, biology, physics, etc.? Also, you may be interested to know that in some countries, Power Balance must state that they have no actual scientific backing for their claims. The Placebo band is just as effective, and much cheaper.
What sort of demo was done at the expo? Was it Applied Kinesiology by any chance? That is a well known bit of deliberate deception.
A quote from the first link (EMPHASIS MINE):
Power Balance bracelets promise to improve balance, strength and flexibility and feature some lofty endorsers: Shaquille O’Neal, Drew Brees and Nicole Branagh, an Olympian from the University of Minnesota. Yet the maker of the $30 bracelets admitted this week that there’s no scientific evidence that the things actually work.
The producers of Power Balance bracelets have sold them by the millions around the globe. They adorn the celebrity wrists of Robert de Niro and Kate Middleton, among others. The hologram-embedded rubbery bracelets “work with your body’s natural energy field” in ways similar to “concepts behind many Eastern philosophies,” the Power Balance website explains.
These claims got the attention of the Australian Competition and Consumer Commission, which compelled Power Balance to issue a letter that was published in various media outlets Down Under.
“We admit that there is no credible scientific evidence that supports our claims,” the company wrote. “Therefore we engaged in misleading conduct.”