I've only just installed this onto my WHMCS installation a day ago. But so far everything is working perfectly.
I use the iWHMCS iphone app and have tested the create and it works just fine. You can create/suspend/terminate and unsuspend using ModulesGarden's cPanel server module.
There isn't anything you need to do once you've changed your server and products to use cPanel Extended.
This is a great way to keep the cPanel password and remove direct access to the /cpanel and proxy cpanel.domain* ... the customer never needs to know what the password to cpanel is.