Ouch. I was put off the petrol version because of the reported high consumption - thats even worse than I thought.
I think we have to stand back and think fact, talk fact, understand fact when it comes to MPG and reports of "I drove from Edinburgh to Brighton on x gallons of fuel.
ALL manufacturers play games with MPG etc. We know (FACT) that mpg figures for any given car are based on laboratory test conditions. These tests DO NOT take into account wind resistance, road variable surface materials, etc. etc. The manufacturer offers sample productions car for testing. The test criteria is known so manufacturers can deliver a production representative vehicle "MATCHED" to delivering best can do performance on the "known/standard test bed.
Put the tested car on a real road, with real wind resistance, real surface profiles, and "real life motoring" and you can toss the "official" figures into the bin.
Please note! I'm not suggesting people are telling fibs about their fuel economy. The poorer the performance the MORE I believe it.
Given a petrol engine then a 1.4 Turbo is roughly equivalent to a 1.8L/2.0L naturally aspirated petrol engine. Both deliver (when in good running order) around 30MPG over the lifetime driving cycle.
For every car I've owned since 1974 I've kept a detailed "lifetime" log of fuel put in, £s put in, Litres put in and all mileages.
Needless to say the ACTUAL figures fall far short of what was officially documented.
Last point. If you want to have a fun, lively, get up and go "drive" then MPG is a mute point. You have to balance dead duck feel against she/he does what I ask. The "ASK" is your driving style and pleasure.
IMHO the 500X is around the expected "level" for a car/engine/etc of this type.
I would prefer to pay some extra £s per year and have driving fun/pleasure than thoroughly hating a £17K+ purchase based on MPG disappointment.
Summary. Lifetime 1.4 Turbo, 1.8/2.0L petrol engines are going to weigh in at around 30 to 35 MPG. Also note that modern engine management systems keep the ideal fuel burn (etc) in the ideal Lambda ratio as best as they can.
IMHO the 500X is no worse or no better than the other make options out there. These manufacturers compete hard to be as good as they can. What one has to do is decide are your a "MPG", "Driveability", "Load carrying", "size", "shape", etc. driver.
Only the individual buyer can dictate/choose the parameters.