Absolutely love the DEF system in my truck, aside from one thing which seems to be a programming issue where it will drink quite a bit when pulling my toy hauler. I get around 1000mpg with normal driving. I equated it to roughly a 4-5 cent increase in the price of diesel, at about $3.70/gal. It's really not that big of a deal, doesn't smell like a diesel, puts out no smoke, fewer emissions, and is sadly cleaner than many gas vehicles. Truck has a gauge that operates no differently from the fuel gauge. I always fill up DEF at the pilot station.
My wife's 2014 BMW 328d also has DEF. They fill it for her at the 10k mile maintenance. Manual says it has a gauge within the NAV, but the option is just not in the system, so who knows how much is in there.
TV: 2013 Ram 2500 4x4 mega cab w/6.7l Cummins
Trailer: 2013 Palomino Puma 27SBU