Yes, a private DNS is useful in some circumstances, but bear in mind, it is another vector of data sharing, you need to trust that DNS service, they have your IP (one more party) and the log of the sites you are visiting, after all, that is their function, to resolve the sites addresses. Proton VPN, Mullvad and IVPN all have their own secure DNS which filters ads and malware, by using those VPNs with their default DNS setting you have more cyber sec, removing one vector of data sharing 

 Yep I'm using Mullvad DNS