If you are printing to an Epson x900 series printer and want to drive the device with CMYKOGcmkk inks then this upgrade is a must. In version 4.1 and 4.5 there were bugs that would not allow the x900HT driver to work properly. Now that has been fixed in version 4.5.1. If you are getting the results you need with your current software using the x900CT driver than no need. If you need to build multichannel profiles then upgrade.