Take one on an extended test drive but you will be lucky to get 30mpg as it’s not exactly aerodynamic.
id say you’ll average around 26 mpg, also if you get the Auto the box changes down a lot to get the thing keeping up with even slight changes of speed not very relaxing.
The good points are they are well soundproofed, for the size there is nothing else as practice and because it’s not massive it still drives a lot like a car (golf).
if you need to load it with gear and people, do motorway miles youll need a diesel in my opinion.
But if you do minimal miles usually with only you in the car and only in town it could be worth considering.