They are great, we have two gen 1 chromecasts and s chromecast audio.
One sits on an older 'dumb' tv to give us all the catch up services and another on the our main smart Panasonic TV as there are a couple of services that there are not apps available for, namely Disney Life.
The Audio is great in as much that it has mean't I can hide all my CD's away in the loft yet still have access to my full music collection as that that all been ripped to a NAS drive, my wife mainly uses it with spotify. On;y downside is the lack of gapless playback support, but it seem's that you have to pay a lot more than the £30 price tag to beat that so can't really complain.