Fitness trackers, while sometimes useful, are considerably overhyped IMO. They're mostly about gamification and the UX inspiring (often inflated) confidence in the results they report, not about yielding fundamentally higher-quality information than online calculators or your bathroom scale or how well your pants fit.

Also, people put too much stock in the 500 kcal/day thing. It's more an example that makes the math work out neatly than it is necessarily something any given person should adopt as a target.