Multiroom: The Chromecast Audio is designed to work as part of a multiroom system supporting most file formats up to 24-bit/96kHz. While it works great with other Chromecast Audio units it will also work with Chromecast built-in products from third-party manufacturers. These include speakers, receivers, sound bars and high-end adaptors from the likes of , , , , and . Create a group in the Google Home app incorporating the speakers you want, and even control it with your voice if you like.
Voice control is the future: Chromecast Audio may not be a special snowflake when it comes to voice control -- most competitors have announced forthcoming support for Amazon's. Google's solution is not only more tightly integrated, however, it's also available now. Using the Chromecast Audio in tandem with the Home is much more rewarding than using either on its own. Tell the Google Home to "Play The Cure on the Chromecast Audio" and it will play you a "best of" from the music service of your choice.
What's not great?
It's not as good for iPhone and iPad users: While the situation isn't as bad as it is with Android users trying to use AirPlay, iOS users still don't get the support enjoyed by their Android brethren. Individual app developers can add Chromecast support on iOS, but that means that Google's frenemies with their own streaming solutions have little incentive to do so. Thus, Apple Music, Apple Podcasts and Amazon Music have no Chromecast support on iOS -- and almost certainly never will.
It has its limitations: While hooking the Chromecast up to a DAC or receiver helps, it can only do so much. It's only able to stream up to 24/96 which may worry some audiophiles, and I had some issues with hooking it up digitally to a Rotel receiver with unpleasantly steely sonics. Also, without a wired Ethernet option you could run up against interference problems depending on the strength of your Wi-Fi (and your neighbors').
Chrome browser support is patchy: While Chromecast is supposed to work without fuss, and usually does when casting video, I found it patchy when casting audio. I was able to cast audio from the CBS All-Access site for a few minutes and then it stopped. No amount of resets would let me get back in, despite it merrily informing me it was playing fine -- this was with a Core i7 PC (the minimum requirement is an i3). Also beware that a Chromecast won't stream from a site that uses Silverlight, Quicktime or VLC.
Should you buy it?
For Android users, the Chromecast Audio is a nearly perfect product, and the closest thing in the world to a no-brainer.
For iOS users, it's a bit more nuanced. If your audio experience isn't on a supported app, the Chromecast Audio is little more than a paperweight. But if you do use a Chromecast-compatible app, it's heaven.
Update, July 21: This review, originally published in 2015, has since been updated to reflect firmware updates featuring multiroom, 24/96 support and voice control.