How is this different than trends.google.com? It's aggregated and anonymous data, not personal data. Their privacy policy is the first result if you search for "fitbit privacy policy". It's incredibly easy to navigate and they clearly have taken pains to make it understandable and clear: https://www.fitbit.com/us/legal/privacy-policy
Don't you remember when they released the movement paths of everyone globally and it was possible to see the location of military bases, based on activity, even though the data was "anonymized"?