Experience using Zanzibar-styled authorization in production?

In particular, with some OSS solution, like Ory Keto (https://www.ory.sh/keto) or Authorizer (https://www.authorizer.tech/docs/overview/introduction), both of which look promising for our use case.

Even though Ory Keto is more well known, Authorizer seems to be a step ahead by already supporting subject set rewrites, one of the key core concepts from the original Zanzibar paper (the lack of which being a major handicap).

Also, how do you manage cascade relation tuple deletion upon deleting the corresponding object/subject resource (e.g. user/group/etc)?