After a month of testing on a in-house server....I have gone ahead and deployed CyberPanel to a working VPS and started transferring accounts from my reseller account (WHM/Cpanel).
So far I have noticed that two commonly used features my clients have are not in CyberPanel.
1). Email Forwarders......these are often setup to forward a virtual mailbox to people. e.g. email@example.com is forwarded to those running events firstname.lastname@example.org, email@example.com. -----but there is no actual events mailbox.
Your implementation requires an actual mailbox to be created in order to set the forwarder (which means an un-monitored mailbox that can get full).
2). A catchall email address for domains.....usually used to catch typos. However, I have clients with seasonal workers and they use the catchall to get correspondence directed to former workers (much easier than managing 100s of forwarders which is what they used to do -- see above).