Sharing an IP address with a load of other people makes one more anonymous. I know there are lots of different ways of identifying someone online but it is a start. My ISP is also behind a CGNAT so I am also sharing that IP with loads of other people and also most ISPs don’t provide static IP addresses so you can’t rely on an that either but I guess I also trust my VPN provider to handle identifying data more than my ISP as I haven’t even given them my name (Mullvad)
Sorry to go on a tangent (I believe it is word of mouth and actions of the company like you say):
What is the deal with Mullvad and Firefox? Are they completely using your services but with their name on it? Would you rather a client directly or through Firefox (bit cheaper now in $ )?