I don't own one, but I know several who do. They love the motor. No issues with it, as good mileage or better than a Cummins or Powerstroke. They all got the truck with the Allison transmission as well. While they don't have over 100,000 on any of theirs yet, I've seen several for sale with over 250,000 miles on them. So at least they last that long, LOL. I know a guy who's got it in a 17ft straight truck on a 3500 van frame, and he says that he gets 500 miles on a tank of gas, with mixed city/hwy driving.
There is a used truck dealer around 70 miles from here that deals in fleet vehicles from trucking companies, construction companies, etc. They seem to sell them as fast as they get them in, whether the motor is in a 2500, 3500, 4500, etc.
IMO, the best thing about them is that they're relatively quiet for a diesel motor.