Using my Chromecast With Google TV as a device for my Spotify speaker group is unreliable. Often it never even works and when it does, it can take 20+ seconds to start playing on all three devices. Once paying, there are frequent occasions when music will cutout for a second or two randomly.
Possibly related: At all times when viewing the Chromecast video signal on my tv, the Spotify progress bar shows the incorrect elapsed time - it appears to be counting up from the time I first started the cast. When using the remote to pause or sync there is a UI glitch that slids up from that bottom and shows a duplicated overlayed progress bars and song title/artist (see image):