I was one of those drivers.
We tracked everything, including prices. The i-CDTi came out on top, above the HCH-1 and HCH-2 and the Prius, but only by a bit. With fuel price considered, it was the worst. We're missing part of the logbook for this car, so I'm not sure about the overall totals.
But... best tank in that car was all the way across California, for 72mpg over about 500 miles.
And let's just say that Jalopnik's measurements are, well, *suspect*. At 100 miles, a short fill can do amazing things for your numbers. (not to mention that they broke some trim pieces off it)
... and
here's what a top-class hypermiler can do with it, with good weather and only one passenger and no time constraints.