DNSthingy’s core value is on-premise filtering with fastest possible performance (i.e. it isn’t a cloud DNS service), allowing you to apply different policies to different device groups. You’re never locked into a one-size-fits-all scenario. An IoT network should not have the same permission as a desktop or mobile device, for example.
However, once a domain is approved for upstream resolution, DNSthingy will send it to the upstream DNS resolver of your choice. This is made very easy with a customized drop-down list like this:
So, in addition to all the DNSthingy services, you can use quad9.net (188.8.131.52) as a resolver of last resort to provide additional protection.