I did this and started to wonder why every web page opened reeaaallly slowly.
Turns out the Pi-Hole Raspberry Pi had borked and wasn't answering at all, my computer was waiting for the primary DNS _every_time_ for multiple seconds before trying the secondary one.
What it should've done (IMO) is query both and pick the fastest.
Swapped to NextDNS and haven't looked back, I set it on my router and mobile devices once and that's it.
Turns out the Pi-Hole Raspberry Pi had borked and wasn't answering at all, my computer was waiting for the primary DNS _every_time_ for multiple seconds before trying the secondary one.
What it should've done (IMO) is query both and pick the fastest.
Swapped to NextDNS and haven't looked back, I set it on my router and mobile devices once and that's it.