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Problems with this type of carrier generally relate to overloading, and load placement. The OEM (or any other) hitch is designed for a point load, applied vertically, approximately 8" from the receiver pin. I have the E53 documents, and the E70 may be slightly different, but the theory is the same. If you have the E70 guidelines, just adjust the calculations.
Using the E53 guidelines, you can't apply the rated tongue weight of 600 lbs to your carrier, unless you can get the CoG within 8" of the receiver pin. If you are 16" out, then you have 300 lbs capacity, at 24" you have 200 lbs capacity, and so on. This is ignoring dynamic effects, and you can see these carriers bounce significantly over bumps.
All the early problems with E53 hitches that I saw, related to bending moments from using cargo carriers. The carriers essentially bent the rear pans of the vehicles, due to the load profile.
When the carrier manufacturers talk about using a certain class of hitch, you need to take into account that your hitch is bolted to a unibody, not a frame, so the bending moments are the limiting factor.
Now, load it up with tents and sleeping bags and so on, and none of this will matter. Put some weight in it, however, and make sure that you stay within the design limits of the hitch mounting.
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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
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