With Add-in Express for VSTO you quickly create a GUI of the Outlook add-in including its toolbars and sub-panes (forms embedded into Outlook windows). Add-in Express includes special designers that give you the following features that VSTO lacks:

• Design-time support of custom Ribbon tabs, Office menu, Quick Access Toolbar, command bars and commandbar controls, menu items, context menu items.
• Adding Outlook options page and folder property pages at design-time.
• Trapping any built-in controls on Outlook toolbars and handling them in your own way instead of the standard one.
• Version-independent event processing for Outlook Application, Item, Items and Folders.
• Context-sensitive binding of your toolbars or their separate controls to Outlook folders or item classes.
• Determining keyboard shortcut processing settings at design-time.
• Adding Action Panes in Excel and Word 2003 and custom Task Panes in Office 2007 at design time.

The crucial thing is that you concentrate on your applied code that automates and handles Outlook objects and solves your applied task.