Right now, BluetoothAdvertisement being ref counted causes problems for clients that do not Unregister before deleting the shared pointer, i.e. the BluetoothAdvertisement becomes "dangling" as the shared pointer is also held by BluetoothAdapter. 
By making BluetoothAdvertisement unique_ptr owned by clients, we can make sure that its destructor gets called when unique_ptr is deleted, which in turn will call Unregister.