If the only need you need is sync repos without exclusions or transformations I wouldn't bother, it could work for you until it doesn't when they archive it or kill it like kaniko or so many other google products/tools.
Gitlab has really simple way to mirror from Gitlab to Github or other git vendors/servers
yea copybara is really for doing transforms in one or both directions.
E.g. translating from external bzl to internal blaze BUILD compatibility, changing between external imports and internal third_party style imports, etc etc.
Gitlab has really simple way to mirror from Gitlab to Github or other git vendors/servers