I pay for mine, not sure how it differs from the free version but you can turn logging off, or if you have logging on you can specific how long to store logs and what jurisdiction to keep them in (I keep mine for a few months in Switzerland). You of course have to place some trust in NextDNS the company that they are actually doing what they claim to do as far as respecting user privacy but I trust them more than Google and Cloudflare, which is what I was using previously.