So ya its "compatible" with Xfinity internet, you don't need an antenna because everything will be streaming from the internet. So you can stop Comcast Cable TV but you need to keep Comcast/Xfinity Internet because this device needs WiFi from your Router to stream these movies and apps. But the movies can't be seen unless you pay for Amazon Prime Video stand alone Movie streaming only or get Amazon Prime for $119/Yr. that includes free 2 day shipping on anything you buy from Amazon, Music streaming and some other additional services.
Also, the Fire TV stick doesn't replace the local channels and even other network channels you get with Comcast Cable TV.
So if you want to watch fake news from ABC, CBS, NBC or CNN this device does not provide that - but for most of us that's a good thing