@Utzer Fitbit's problem is that you can only connect it with the official app which syncs your stuff with their cloud iirc. So if privacy is a criterion for you, I would check #Gadgetbridge and look which trackers are compatible and work fine. I've got a Xiaomi Mi Band 4 and while it works with Gadgetbridge for step counting and heart rate, some features like tracking bicycle trips do not work at all.