It can not connect to other Google cast products. The software could use more features. When connected works good.
I connected Chromecast audio with Bose Cinemate 1 SR home theater using optical fiber for my home background music. Source is Spotify. Excellent sound quality. Cons: no much software support Chromecast yet.
Finally... I can stream music to my surround sound without having to have the TV on. CastTab with the original chromcast would "work" but it was choppy when I would use it while working with needy software. This solves it all. Only downfall, does not work with my Tab 2 but it works great with my G4.
Picked up three of these babies for around $100 total. Setup was super easy using the iphone chrome cast app. Can stream NPR, Spotify and Google music straight from the internet - frees up phone to make calls, text, etc. Can also use Google Cast extension for chrome to cast audio to the device. Has analog and digital optical out (same as on Apple Airport Express). Sound is very good (make sure to select the HDR audio in settings). Currently, software does not allow for "multicasting" or selecting multiple devices to play same music, but it is promised in a future update. Does not support direct streaming of Apple Music. Overall - a great way to turn a set of speakers into a makeshift (and cheap) Sonos substitute.
Audio version! This little guy works very well with so many apps out there. Just plug in the 3.5mm into any audio source (speaker system). Then use various apps to connect. Only thing that is no good is how Spotify on a computer (desktop or laptop) requires you to connect to the Chromecast on your phone's Spotify app first, only then does Spotify work with it on the computer. It is important to note that this is entirely Spotify's fault, though, since it is their software. So 5 stars all the way for the Chromecast Audio and its capabilities! Note, the regular (video, not audio) version is completely different in terms of what and how it connects to various electronics. This audio version is for audio only (duh). No HDMI or anything, just a 3.5mm wire.
Forget Bluetooth. This is so much better. Uncompressed high quality sound that does not drop out. I downloaded Google's Play Now program on my PC, and it grabbed my entire iTunes library and loaded it up into Google's cloud. Now I have got access to all my music, plus tons of other music -- all at high bit-rate and uncompressed. Hookup and use are simple. My wife loves it (she never never used Bluetooth). When their multi-room software update comes out in a month or two, it is hard to see why anyone would choose a more expensive alternative. A true giant-killer product for 35 bucks.
Chromecast audio is amazing and multi-room setup is a huge plus. Just like with video, you cast sound to the device. At the same time, you can create a group of devices that you can stream music to at once. So, instead of having very long cables and mixers, sound comes out of multiple speakers. It all works well without lags and without problems. The sound quality is also good and supports FLAC. If you like using lossless, it supports FLAC output directly. The only pain is the software setup. If you use google play, spotify then I suppose it is straightforward to just set it up. However, if you want to cast your own flac, it is a little tricky. It requires BubbleUPNP and a UPNP server. I have a hodgepodge of UNP server from Plex and BubbleUNP working for me to cast my FLAC files. For most using Google play, I think the standard stuff would suffice. Overall, if you listen to a lot of music, this is a good product. I have uPNP music server with FLAC files to listen to. Other people might prefer Spotify and Google Music. It solves a unique problem. On the other hand, this is not a necessary product. I guess I could listen to music on my headphones and walk around with them with music everywhere. But, if you spend $1000s of dollars on audio equipment and would like all sort of stereo configurations, this will be a very useful tool for a low cost that works easily. You could use raspberry pis and other complex products but there are just too many things to do and configure. Setting up the Chromecast Audio takes 2 minutes.