Thoughts from someone who has actually driven one:
You have to view it as basically motorcycle mileage but with two Passengers and a tiny bit of cargo. It's a bit loud but lots quicker than you'd think. I've driven one on the Autobahn dozens of times without problem. It'll go maybe 145 kph floored.
The diesel gets 50 mpg and the gasoline engine somewhat less. They have much more head and leg room than most compacts. They are the safest car in the micro-class and are actually much safer than nearly all other cars in the normal compact class. The body is built out a sort of cage, apparently like race cars. Like I said, it's motocycle mileage with small car safety.
Basically if you need cheap urban transportation and have another car to do the shopping, this is a great (and super cheap) alternative. If you need a great big SUV to drive the kids to soccer, or to compensate for a small penis, then you won't want this one.
How much does the other half of the car cost?
Beep, er, I mean, bump.