Own both. Drag down on notification screen and hit mirror screen and works the same way as slimport on chrome castTwo different devices, with two different intended uses.
Chromecast is a streaming device. It requires internet, and a "controller device". You can't run straight chromecast with just the 1 device. It gets URLs handed to it, then it does the streaming itself. (Sure, there have been various apps that allow you to mirror your screen, but that's not how it was intended to be used)
Slimport is a straight video/audio output. Everything you see on your screen shows up on the TV you're plugged into. This is a much better option if you intend on using your tablet like a PC with a keyboard/mouse. You don't need internet, you don't need wifi, you don't need another device to act like a "remote control". It's straight up video/audio out.
I own both and I use slimport more. It's just less hassle. You plug it in, and that's it. With the Chromecast, you gotta find wifi somewhere(or create a hotspot) and then run the setup app on a third device (Chromecast, phone for hotspot, and tablet for remote control) that's too much work.
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