On basic MSI I'm trying to display a MessageBox after the Finish Dialog, I have created a Custom Action and tried to add it to the at several locations at the end of the UI and Execute sequence, But it's not displayed.
You may try adding a DoAction control event to the Finish button of the SetupCompleteSuccess dialog to run the custom action that displays the message box (setting the condition on the event to 1 if you always want it to run at the end of an install operation, or Not Installed if you only want it to run at the end of a first time install).
