LDK vs. SLU

Both the Licensing Deployment Kit and the Server Licensing Utility perform the same function of registering the Runtime license for the system on which it will be run. Both are provided in order to give you some options.

When installing the license, the user you are running as must have Administrator access so that the Registry can be accessed and the license can be added to the system.

If you are deploying to your own systems (e.g., for enterprise IT staff), the use of an Accusoft branded Server Licensing Utility may meet your needs. Similarly, if you handle the deployment onto end users systems, you may also find the Server Licensing Utility to be sufficient.
If you wish to hide this licensing registration from end users, you will likely choose the Licensing Deployment Kit, which allows you to integrate the registration process into your application. The Licensing Deployment Kit also allows for the optional assignment of Access Keys to specific users, which lets you manage your licenses more directly and limits the distribution of licenses.