I've been an avid user of Add-in Express for Microsoft Office and .NET for years and couldn't be happier. I first used the tool to build an Outlook add-in for a large bank in the USA. The Add-in Express toolset solved all the major risks in the project: support for multiple versions of Microsoft Outlook, non-admin installation, and working with the Outlook Security Guard. Add-in Express handled all of this plus made many other tasks super easy thanks to their visual designers.