You can use the Preview Formula Wizard window to see what an add-in function will look like in the Excel Formula Wizard.
The Excel Formula Wizard is quite restrictive about what it will display. Under some circumstances it will display an extra full stop at the end of a description, or it will truncate your text. The preview is very similar to what the user will see in Excel.
The precise layout of the help in the preview window follows as closely as possible the layout of the Formula Wizard in Excel 2007.