I was driving the ML when we had it. It was a great car on paper for me. After driving it, I realized it was a chic car. Wife had a Denali...and she wasn't willing to trade me. In retrospect I wish I would have twisted her arm a little more to swap. If so, we'd still have it.
Got the A6 and absolutely love it. If the thing had apple car-play and was a manual transmission it would check every box I have. Even without those two things, its about as close to perfect (for me) as it gets. I miss the pre-fix behavior of the engine and tranny, but the big check from Audi was too much of an inducement not to fix it. We recently traded in the wife's Suburban for a new Yukon for her. While I was tinkering with the Yukon, putting on some bells and whistles, the wife started driving the A6...almost one year later, she's still driving the A6. I can't get it back from her. For her not being a gearhead, she gets her pick of the cars around here. LOL!
If I were driving it, it would be tuned and then some. With her driving it, as long as I keep the DEF full and make sure I put in some stanadyne in the fuel tank, that's all the special treatment she gets right now. I've spoken extensively with Owain from Malone and will, some day, have it tuned by Malone and likely add some offroad components from Darkside.
In theory these diesel exhaust cleaners are a good thing. Practically they have been a PITA for everyone. With fuel rail pressures where they are these days, I bet the 3.0l diesels would pass a breather inspection within normal operating limits. However the emission inspections around me are all OBD-II so its an immediate fail if equipment is removed. If something reasonable happens with the emission inspections around me, in addition to the A6, I'd have an A7 (for me this time), and two Q5s for my soon-to-be drivers in the driveway. The low-end torque, efficiency, and creature comforts are just too nice not to have a fleet of 3.0L TDI Audi's.
So right now, I'll have to live vicariously through you and Trae if you get yours tuned or tuned and deleted. (BIG SIGH).