As a one-time developer of consumer IoT hardware I’m divided on this. In principle everything should respect the DNS servers provided by your local DHCP server.

As a one-time developer of consumer IoT hardware I’m divided on this. In principle everything should respect the DNS servers provided by your local DHCP server. In practice some of those DNS servers are hilariously bad, because they’re operated by ISPs, who will happily highjack every single DNS query to inject a message about how you’re approaching your bandwidth quota, or just outright ignore TTLs that were dropped to allow clean switchover between providers. We ended up hardcoding known good DNS servers because otherwise we’d get complaints from customers when things stopped working, and no amount of saying it’s not our fault would avoid being branded as useless crap.