How bad is a Apple watch for privacy

My roommate gave me one for free as they got a new one, I’m kind of intrigued because well it’s free, and I’d really like to be able to log my running/cycling and use my phone less, I know it tracks loads and sends some to medical facilities etc, if that is anonymous like it says that sounds good, but how nefarious is the watch?

apple apple watch bad cycling etc free kind log medical phone privacy running watch