Good to hear!
If you need to use it in another situation (not needed for this one), the User Data Passed to Handler just passes whatever you type as a string into the sAlertData variable, which is a List of Strings. The whole string you type in the alert configuration will be one of the items in the list.
For example, if you were to type
testdata|testdata1|testdata2, then in the aAlertData list you would see an item
ININ.CustomHandler.UserData|testdata|testdata1|testdata2