The thing about chromecast dongles is they integrate with Android. You kind of have to use it with Android if you want to just stream easily with Apps. It is kind of amazing. Be it photos, Netflix, Tubi, … Just open your mobile app as usual and hit the streaming button. You can even disconnect your mobile device in many cases after streaming starts.
Privacy. Have no idea, but my default assumption is not so good like most Google products. Wish I knew exactly.