Chips are generic, they are programmed for various stages of tune, and they are relatively cheap. But each individual engine won't be optimsed as the fuel and ignition maps allow for safe running to account for the variation between engines. A proper re-map will be tailored to your engine for best running, most power, and/or mpg.
I guess if you want the best out of your engine, you need to cough up for a mapping session.