Yes, usually manufacturers use rebadged towbars for their OEM ones. For the GK3, the OEM hitch should be not a Westfalia, maybe a Brink...
Anyway, in Italy I would pay 800€ for the OEM towbar, all inclusive (towbar, fitting, burocracy): the Westfalia should be moreorless 300€ cheaper... So no doubt about it, considering that the no-oem is completely hidden when removed.
And I cannot make a DIY installation... In Italy we must pass a MOT visit, and officers want a declaration of the mechanic about the correct installation.