I guess you are talking about the RS-tuner kit from fastchip.
City driving it's about 1:10 (Litre:km) you do the math. Used to be a tad more economic, but when you compare to other hot hatches it's still running cheap.
Highway driving (holland-germany-austria) complete was 1:14 and that was not hanging about. germany the average speed was about 100mph and playing audi's / volkswagens / bmw's.
Ow am running an adjusted ron98 map which is a bit less economic then the more generic map.
To measure you should be driving with both maps with CC which I do not have and identical conditions. I guess there can be intresting results, since the engine is more efficient.