Anything I've heard of the small airtwin engines suggests they actually use more fuel as they have to be driven harder.I drive a 1245cc Panda at the moment with the old bombproof FIRE engine in it and it is very economical.
For my previous car I thought I would try a Skoda Fabia 1.2 as they are supposed to be ultra reliable.Nothing could be further from the truth.
From rollbar bushes at 18000 miles shockers every 30000 miles and wish bone bushes,power steering rack and gearbox at 60000 miles amongst other things. The final straw came at 80000miles when the starter was acting up and nobody could supply one, even the dealers!No one had seen one like it.
My biggest concern was fuel consumption,My very best was 50 to the gallon at 50mph on the motorway which is down right dangerous, average was 32 mpg but if I used air conditioning it dropped to 21!! That was a 3 cylinder engine.
When I changed back to Fiat the saving in fuel actually paid for the car over three years.
My wifes cousin was running a diesel Fabia and he reckoned it was well short of the figures quoted,around a third short if I recall.