Custom to the car? lots of threads on "custom" maps. Search.
A custom map, if it really is custom, is only effective while the conditions are exactly the same as they are on the day of the remap. Change air filter, use different petrol, drive it on a hotter day etc etc and its usefulness goes out of the window because it wasn't mapped for those conditions
- however - custom remaps usually aren't that custom anyway - meaning they're probably no better than a good generic map thats adjustable.
But for the price, its a still a decent remap from what i've read.