I've got the X2 - we had the old halogen version, but it suddenly stopped working after having only been used a few times. Fortunately it was purchased at REI and not only do they have an incredible return policy, they were aware of a problem with the model that we had.
My hubby was totally irritated when I came home with a new light instead of getting his old one fixed (ahem who was the only person in the house bike commuting at the time.....), until he used it He's since "forgiven" me and bought another one for himself.