The question of fuel economy always seems to come up when people look to switch from what they currently have (normally diesel) to a petrol Cupra/R
If you are honestly bothered then stick with what you have, if you always have one eye on the petrol gauge there really is no point in owning one.
I personally don't think it is bad but then I've always had petrol and couldn't really care what mpg I get, that's not the reason I bought the car.
My figures would be.
Steady driving off boost = 35+
Hard driving 15-21
Normal driving with the odd squirt 25-30
You're unlikely to want to drive the car in such a way that you get the 35+ constantly, so in real world terms I'd say daily you'd look at around 28mpg (dependant on the trips you take)