I've started using Owners packages instead of Herald rules. Owners packages are generally more powerful when a package spans multiple repositories or when the repository structure is likely go change (in which case regexes for Herald rules would need to be updated... Actually I'm not sure if Owners packages paths are updated when files in the package are moved, but it is certainly possible).
One thing that's great about using Owners is that I don't need to setup a Herald rule for auditing unreviewed commits, I get this functionality for free. I do, however, still need to setup one or more Herald rules for Differential, to add blocking reviewers when packages are modified. It would be great if Owners could support this use case natively.