Bluetooth is always on for Mi Band 2 to notify me on calls/SMS with vibration. My phone is 24/7 in silent mode (alarms only) and not always in my pocket so having "vibration-only" wearable device is very useful for me. Sorry I didn't mention that.
I've reset Advertising ID and then enabled "Opt out of Ads Personalisation" in Google settings.
I've also disabled Mi Services "Send diagnostic data automatically" & "User Experience Program" (Xiaomi is this device manufacturer). I hope I don't miss something.
Upgraded from Mi A1 to Mi A2. Both devices are in Android One program which makes them appealing for me. Mi A1 is given to my family members who was using a seriously outdated 2014 device.