Hi, I have a 2010 Ml350 and the V6 is pretty solid apparently. Other swill know more. I don't do big miles often 10 mile(ish) trips often less, but steady. I seem to be averaging hi 20s and often 30plus MPG. As example got back after several short trips yesterday and had averaged 31mpg during day. Not a car for decent mpgs but Its not much different to my last 220 E class. Oh and I love it! 
Ours is a 2012 W166 350 (TBH I don't know what the difference is between the B/E and the B/T), only had it for a year, but we cannot fault it at all. Does everything very well, and build quality is spot on.
One thing I would say, is they are very very few with any options on at all, even folding mirrors was an option!!
I paid a little over the odds, for ours but it had nigh on everything on it I was wanting, which obv comes at a premium.
One thing I would say, is they are very very few with any options on at all, even folding mirrors was an option!!
I paid a little over the odds, for ours but it had nigh on everything on it I was wanting, which obv comes at a premium.