Oh, you must also consider that NextDNS is American, and legally their government can force the company into cooperation, such as providing a backdoor to monitor all traffic, while placing them under a gag order. If you only want to avoid ads and tracking, that’s fine. However, if you’re concerned about government surveillance, that’s something to think about before using American services. I wonder if such U.S. policies influenced the creators to abandon NextDNS and start a new one in EU… Lavabit creator chose to end his service and close the company before complying.

HaGeZi compiles and maintains the biggest DNS blocklists around, it’s used by several DNS services, and most likely by all of them but they don’t credit him. On his page, he recommends some online services based on transparency and privacy. He used to recommend NextDNS as well, but he removed them because, for a long time, many people have complained about a lack of customer support - they don’t respond to any contact. It seems like the service is running but is somewhat abandoned. Its two creators started dns0.eu and are probably focused there.
Technically, the only issue with NextDNS is that it’s unmanaged, and as for now there hasn’t been any changes in who are providing the lists, it just works.

NextDNS works because it uses several public lists, but it’s kind of abandoned and HaGeZi removed it from his recommended DNS services because of the complete lack of customer support. The guys from NextDNS moved to dns0.eu. You can set Mullvad’s own DNS service in the browser, and being an ecosystem specialized in privacy, a much bigger company, and having curated lists instead of just shoving tons of public lists without checking for duplicates (NextDNS), correct me if I’m wrong, but I think Mullvad’s DNS probably offers a more concise service.