Temple vs Fitbit
Fitbit is a device plus an app. Temple is the reading layer that works across whatever you already wear.
Where each one fits
Fitbit ships hardware and the software that goes with it. Temple starts from the other end: bring the device you already own, and Temple does the interpretation.
That matters if you have switched devices, or use more than one. A history that lives inside one manufacturer ends when you change brand.
Your data stays exportable and readable. Temple is a place to understand it, not a place it gets locked into.