Hi, the extlib release zip contains these 2 updateSite zip files:
updateSiteOpenNTF.zip
updateSiteOpenNTF-designer.zip
It sounds like you installed the updateSiteOpenNTF.zip into Domino Designer, instead of the updateSiteOpenNTF-designer.zip file. The updateSiteOpenNTF-designer.zip file contains extra plugins that provide the graphical representation of the control, and the Properties views panels.
Try updating your Domino Designer install to add the contents of that -designer updateSite.