There's a long line of stuff involving these bracelets. If you get near any salesman they'll talk about "controlled studies". Yes, they have controlled studies, but they're not peer-reviewed or published, nor are they double-blind. Their methodology was to have athletes perform a feat twice- once without the bracelet, and one with the bracelet on. They only ever wore the bracelet the second time, so there's a measurable warm-up bias in the bracelet results.

In double-blind experiments, there is no statistically significant difference between the bracelet and a placebo. On the other hand, some people respond really, really well to placebo.