If you read the details of this thing all it really is is a wifi connection that forwards an HDMI signal to your TV. They've just abstracted a software layer that Google can control to channel you through their portal. It lets them set a standard that other companies have to abide by if they want their content accessible from Google's device. They package it to make it easy for the consumer, but it's really just an example of Apple style content control.
Seriously. You can do the same thing with any laptop/desktop/phone/tablet with an HDMI-out port, and without needing a proprietary device!
A month ago I had the task of figuring out how to get an Android (4.1) screen onto a projector. The easy option was to do a microUSB-to-HDMI cable. That sort of worked, but the odd thing was the screen would sometimes flicker and disappear temporarily. Some research brought up speculation that the HDMI screen capture mechanism wasn't synced with the screen refresh.
That version of Android didn't support Miracast, and attempts to get the phone to share its screen wirelessly with the projector weren't working.
We were, however, able to get a Mac's screen to display without the flicker problems, so we tried to get the Android screen to show up on the Mac. I got a VNC server app working on the phone but none of the VNC clients I could find supported landscape-mode display for some reason, so that was out.
I eventually found a solution, droid@screen, which basically does screen capture over adb (android debug bridge). That worked with the downside that the projected display lagged by a couple of seconds (didn't happen with the direct HDMI connection) and occasionally the whole thing stopped working until adbd was restarted on the phones (sudo pkill adbd).
The point is, the task of showing one screen on another isn't as seemless as it ought to be on all devices, so anything that provides more alternatives for doing that is welcome.