I just bought one since we only get crappy analog reception for FOX and it just wasn’t cutting it for Cosmos. So I bought a Chromecast so I could cast Cosmos from fox.com to the TV. Cosmos in HD - yay!
We have a smart TV so we can watch Netflix, Amazon, Youtube, etc. through our TV. If it hadn’t been for Cosmos, I would have been perfectly happy without the Chromecast. I will say that it’s much easier to pull up a Youtube video on the tablet and cast it to the TV than going through the terrible TV interface. Some apps (like YouTube) are already configured to work with Chromecast so it’s pretty straightforward.
And apparently the Chromecast extension for Chrome is only a beta version and is quite buggy. Google and you will get lots of examples of people not being able to cast from Chrome. I had problems at first, but somehow it is working now. There can be issues with wireless modem compatibility too. Plus, you can’t get the Chromecast extension if you are running Chrome on Android. I ding Google pretty hard for that - It’s their own OS, for chrissake!
TL;DR: Handy for playing videos from your Chrome browser, but only if you are lucky enough to get it to work properly.