Still can't understand why the Sigma Rox would be better than a Garmin Forerunner 305 + cadence sensor, which will do everything the Sigma does, plus give you GPS mapping and very robust integration with various online and offline programs, which have been tested by hundreds of thousands of people. For equivalent money, and possibly less. (A LOT less if you decide you don't need cadence.)

Plus, the Garmin305 Forerunner can be used for running as well.