However, 9.9.9.10 does not perform DNSSEC validation, as 8.8.8.8 (Google), 64.6.64.6 (Verisign), 9.9.9.9 (Quad9), and now 1.1.1.1 (CloudFlare) do, so results may not be as trustworthy.
My personal experience is that I had reliability problems that I didn’t have with Google. And DNS is a critical step in the connection for which you really want reliability.