The NuForce rear step towbar has a capacity for towing of only 1500kg.
It looks like the old MCC/Ironman bar which had a similar rating. I had one of those on my ML and clearance was very good. The tow capacity didn't worry me since I don't tow heavy anyway. Possibly not quite as heavy duty as the ARB, but did the job well for me.
This will give you an idea of clearance, on the ML. Obviously won't be quite so good on the Serena Williams equipped MN.