That is because it appears to attach the same way the aftermarket hitches attach, to the sheetmetal at the back of the vehicle. If it actually includes longitudinal struts to replace the OE bumper shock absorbers, please advise because the site you listed doesn't show those in the photos.

Much safer to go OEM from a structural standpoint, but if the style of a hidden hitch is more important to you, then it does look clean.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue