I’ve been looking at this recently and had read* that the Chromecast Audio optical connection gave a better sound quality. Also if you are streaming Spotify say you remove the Bluetooth element which also compromises quality. Mind you I don’t know if you can stream music stored on your phone to the Chromecast.
TBH, my (not cheap) bluetooth dongle went back after a week. Having to run something on the phone then bluetoothing to the stereo hammered the battery, moving around the house with the phone in your pocket lead to all sorts of drop outs, pops and buzzes. Anyone calls/texts/messengers/whatsapp and you occasionally have issues with drop outs and so on.
Sat on the sofa listening was fine. But then i’d just have put a CD in.
Got a chromecast instead. Just tell it what to run, and it sits there and does it. Over the wifi rather than hammering your phone. You can apparently cast music that is stored on your phone to the chromecast if you want. But not something i’ve tried. As all mines on a server and linked through my spotify account (or Plex, or a couple of others, depending on what i’m using to play it!)