We used ns1 at my last job, they were indeed great to us. We moved from self-hosting DNS because the DNS servers would randomly become unresponsive and would start returning fake records. After switching to ns1 and getting our first bill, we realized that a lot of our network equipment apparently did a DNS lookup for every log line. This resulted in an exceedingly large bill, which ns1 happily reversed (we did fix our stuff ;).
Since then I've started using CoreDNS, which does seem easier to monitor. (I don't know if it's faster or more reliable, but it has a lot of ways to figure out what's going wrong. As it turns out, DNS causes people a lot of trouble these days when they use it for service discovery, and their services discover each other hundreds of times a second. So that's why DNS servers grew APIs and observability features.)