I am using NXDOMAIN removing now live and having to still testing specific things. I had to adapted a lot to make it ‘user proof’ and is also near future proof for Pihole.
I am everytime impressed how fast, huge lists are checked or edited when using linux tools. And this on a RaspberryPI.
I was only checking for NXDOMAIN and I going to add SERVFAIL so that is also becovered.