Hi Jill,
The challenging part is the authentication against the SAP web service. Duet Enterprise provides the single-sign on from SharePoint to the web service. Once authenticated to SharePoint the user can now access SAP data through the web service via SAML authentication (for DE 1.0) or X.509 authentication (for DE 2.0).
Furthermore Duet Enterprise provides supportability features (e.g. via a correlation id you can do troubleshooting from SharePoint to SAP) and comes with out of the box features like Reporting and Workflow. Please take a look at our Self-Pace Learning material, which provides an overview as well as in-depth discussion of these topics.
Cheers, Alex