Pi-Hole or the adblock package for OpenWRT are probably better examples. GL.Inet routers are already natively supported by OpenWRT (since their firmware are just custom forks) so one can flash them.
Yes, theirs is a custom fork. Only commented about flashing to vanilla OpenWRT in relation to your comment about being spying concerns (and since some, including myself, aren't that comfortable with their remote cloud service built into it).
