If it was good, it could be better.

The plugin is well intentioned but needs careful and clean programming. After registering fields and completely removing the meta box, the slugs remain dirty in the database, making it impossible to register them again.

It takes time to enter the database and delete them by hand – IF you know how to do this – then be careful when naming fields and using the plugin. You can end up with “customers”, “customers_02”, “customers_03” and so on if you need to recreate and refine your meta boxes.

Summary: A simple rollback cleanup in the field creation process would resolve the issue and avoid future headaches.