It was my understanding that this vehicle is designed to detect sway etc. by its advanced electronics and counter by alternating braking to/from the opposing side similar to the lane-following function.
Sure you read your owner's manual as this was also a concern of mine and it is addressed in there.
Expect others will also chime in.
Yes, that is what M-B says about their advanced electronic controls which compensate for a shorter wheelbase than one would expect to be stable when towing. But has almost nothing to do with trailer brake controllers (TBC). Last March I was seriously considering a W166 and had to teach the salesman about trailer brakes and how his M-B magic technology was nice but did not address the issue nor the legal requirement.
In some states a TBC is required for trailers as light as 1200 pounds. Required by most states by 3,000 pounds.
I have towed a 1,000 pound trailer about 4,000 miles with my ML, and a 4,000 pound trailer about 1,000 miles. Strange the symmetry there. Can't say I have ever known the fancy anti-sway algorithms to kick in.
Have a Tekonsha P3 TBC. Haven't found a satisfactory place to mount it. My legs run very close to the panels under the steering wheel. So far I have taped it to the dash to the left of the driver's instruments near the HVAC vent. While this is a very good TBC I don't think its function is as smooth or transparent as the built-in unit found on my former Ford F-250 which I used to tow about 20,000 miles.
Have considered cutting the lower dash panel to mount my TBC mostly inside the dash but am not yet ready to make such a major mod. Concerned about the cost of replacing that panel to undo the installation.