It's a pretty cool idea and for the price it might make a good stocking stuffer but I do have a few observations.
While the image above is reasonable it's missing the power cable. When I initially discovered the Chromecast audio I was under the misconception that it might be battery powered. (looking back at the Chromecast I should have realized that).
The main use-case requires a WiFi connection for all of the devices to communicate. There is a "guest mode", however, I do not know if the device needs to be connected to a WiFi network to enable that mode. In other words is there a "hotel mode" so that I can bring it with me on the road.
In the meantime it's just fine around the house but it's main use-case might be statically connected to the home stereo.