The basics of how ERRP is implemented are good, though we're missing a little flexibility.
One thing that can be improved is the e-mail that goes out to the admin-c. We have customers that purchase domains on behalf of someone else, which means the admin-c would receive an e-mail that is addressed to the account holder in WHMCS. I would rather have a different e-mail that is used for ERRP notifications with different variables. Next to the already available variables we would like to know the admin-c' name for example. That way we can properly address them.
This could be partly done with variables alone, but we should try to avoid complexity in our e-mails.