I bought an XO and rode it until it broke. As for the above comment about the X9 being stronger.. they're virtually the same derailler. The X9 lacks the various titanium hardware and spring, but they both still use a composite body which keeps them reasonably light. The composite is also probably stronger than any of the metal pieces, and I have a destroyed XO to prove that statement! As for the shifting feel.. lets just say after I broke the XO I didn't buy another. Simply not worth the extra money for the type of riding I do, and I really can't tell a whole lot of difference between the two. Both are fast and firm.