I wouldn't use this for my own moral reasons but we have different definitions of free. In this case you use "free" to mean: providing personal data and being subjected to a targeted marketing campaign in exchange for music.
Using youtube-dl circumvents both the personal data and the marketing. Just convert to audio with ffmpeg, and then you can listen on your own devices with a normal music player.
Using the flag shown at https://askubuntu.com/questions/423508/can-i-directly-downlo..., you can see all of the different stream qualities available (both audio and video). Some videos (particularly official music videos) have pretty good audio, while amateur videos, remixes, and parodies usually don’t sound as good.
I haven't really thought through my moral position in detail and I probably wouldn't answer this even if I did. I'm just a random person on the internet.
"To provide you with features, information, advertising, or other content which is based on your specific location."
You might also be interested in the massive amount of data they store about users that was discovered after GDPR passed. Here's the HN thread: https://news.ycombinator.com/item?id=17681289