A little more delay compared to Bluetooth but better sound.
I wanted to stream audio to sonos and watch a movie at the same time, but it is too slow and has a delay. For only music isvery good!
When I bought Chromecast Audio I thought that it will be very bad in sound quality, and that not is true. The only thing that I do not like is that when I see videos in chrome browser, the audio is delay by 1 or 2 seconds. Nevertheless, it is worthy for $35.
pro: good for multi-speaker synchronization casting easy to use works okay for primary purpose cons: does not have bluetooth --- meaning will not work with music that do not support google cast (except android) for music streaming with android, the packet loss ( from interference) is much worse than bluetooth. I believe this is due the inherent design of WiFI vs. bluetooth (more resistant to interference). However, this makes music streaming, even with android, pretty useless. when trying to streaming audio of a video, there is always a delay, unlike with bluetooth the above mentioned flaws makes this device extremely limited in usage scenarios -- i.e. if you only want to listen to music with google-cast only app, then it is okay. if you do not need multi-speaker synchronization, do not get this device.
I have 4 of these connected in my house: living room entertainment center, office computer speakers, line-in to a bluetooth speaker in the bedroom and a cheap amp to some outdoor speakers. Using speakers that were already in my house, I now have full house audio for a $100 investment!!! I have admired Sonos for about 10 years now, but could not justify the cost of buying all their speakers. Chromecast Audio provides full control over what speakers are in what groups and the volume they play at. I have grouped adjacent rooms, whole house, etc. and its great to walk from room to room and not detect any major delay in the audio. My only gripe is that I wished this functionality worked with my video Chromecast.
I now have 5 of these in our house to replace/hook into the bluetooth speakers we had in each room. They work extremely well for any app that supports casting to them (almost all apps), and they can mirror your device's whole audio for apps that do not. They are not the perfect solution though, there is significant lag when mirroring audio, which makes them unusable for trying to watch video on your device's screen and audio over the chromecast. They can also be occasionally buggy at times, but overall, work very well. The main reason we got them is to avoid having to track down which device is connected the bluetooth speaker, then disconnect it so yours can connect. With Chromecast you can simply "cast" to the speaker and it will override what is playing currently. The audio quality is excellent for apps that support casting. Others can control volume and play/pause what is playing on any of the chromecasts through the google cast app. I do wish the google cast app was not so content-centric and defaulted to device-view first.