Thanks for setting up this feature discussion @robb.
I have used squid and web proxies in the past but moved to DNS filtering as I found it a more reliable way to categorise and block sites.
I did actually install it on a clean NethServer today. It is fairly trivial using the RPMs IF you install (eg) webtop first - thanks to the webtop_team who have covered the installation of java etc dependencies. I disabled NethServer dnsmasq, changed the nxfilter GUI ports and adjusted the firewall etc. Worked perfectly.
The next step was to re-instate DHCP services, yet, by then, I realised a better solution would be to install in a container: https://github.com/packetworks/docker-nxfilter That, again, was reasonably trivial to install with nethserver-docker (portainer).
This way, NethServer is intact and its DNS is simply pointed at the filter. This project can then likely wait for Portainer to be more production ready.
Having done all that, I did find another DNS filter that, I think, would be more suitable for native integration into NethServer, Pi-Hole: https://pi-hole.net/
As time permits, I’ll set that up and compare the options.