For fun (and out of curiosity) I downloaded and ran Steve Gibson's DNS Benchmark program. It compares a number of well known DNS servers for performance running a number of types of queries. I'll spare you the tabular results (they'd be different for you anyway). Under the "Conclusions" tab, there are informative paragraphs describing a number of findings. These are the headlines I found interesting:
(Red X) "System has only ONE remote nameserver configured." That's because I only have one Pi running Pi-Hole.
(Green Check) "System's sole namesever is alive and replying to queries." Good to know my pi is working 
(Green Check) "System nameserver is faster than ALL public alternatives." (And I'm on a Pi Zero W over wifi)
(Green Check) "This system's nameserver is 100% reliable." (Meaning no dropped queries.)
(Green X) "This system's nameserver intercepts name errors." (In response to invalid DNS lookup requests - part of the filtering?)
(Green Check) "System nameserver is replying to all query types." (Gibson uses three query types.)
It's an interesting utility. More here: