This is a maintenance release which fixes all the (known) problems with the autopilot and navigation system. It is a complete installation, not a patch.
It also introduces a change to the course indicator, which no longer points to navaids or waypoints. That functionality was really a remnant of the very earliest version of the panel, and not realistic at all. The heading/course indicator is now just a basic HSI without VOR indication.
Please note that this is not a separate version, the installer will overwrite the 4.1 files in the same folder and will show as 4.1 in the FSX aircraft selection dialog.