The wearable fitness/activity tracker landscape is analogous to the health IT work of electronic health records (EHRs). There are challenges with the interoperability of data. If you use a Fitbit, you can share data and compete against other Fitbit users. If you have a Jawbone UP, you can't operate within the Fitbit ecosystem. Although these trackers may collect similar data like total # of steps and calories burned, they run on proprietary sets of data living within their own ecosystems.
Some trackers and fitness apps use an open API so that you can link your data with other health and fitness apps (like Google Fit or Apple's Health app). Under Armour is probably leading the pack since MyFitnessPal and MapMyFitness both integrate nicely a number of wearable trackers and fitness apps. In some instances, you may end up with duplication of data (especially if you are using several platforms).
There's another option for those of you who are serious about quantifying your data: Tictrac
Tictrac syncs with the activity trackers and fitness apps that you already use. The Tictrac platform delivers high user engagement because it has been developed by a unique team that combines practical expertise in user experience design, behavioral economics, data science, and predictive analytics.