The core of Chromecast is its own Chrome browser.
When you cast from an Android device using one of the supported apps, it gets content at the highest resolution - it's not a mirror.
You can cast Netflix and then go off and do something else while it's playing. In fact, you can kill Netflix, reboot your phone and it will still keep playing.
That's the difference between Chromecast and Miracast (aka All Share as Samsung calls it).
I've found that the picture quality with Netflix exceeds that of the Netflix app built in to a Samsung SmartTV.
Please visit our Chromecast forum for more details.
Cheers!