You know what they say, right? You can never have too many fitness trackers. After coming out with two health monitors back in September, Fitbit is back with a third product, the Flex -- a waterproof wristband seemingly designed to compete with the Jawbone Up. (In PR speak: "Fitbit understands that one tracker does not fit all.") Like other Fitbit devices, it counts calories, steps taken and distance covered (but not flights climbed). It then automatically sends that data to a personalized
