A generic chip should be more conservative in it's boost and ignition curve to take into account normal wear and tear etc and all the unknown variables of engine that has been through several owners and is a high meileage.

A live map can push the engine to it's limits, as you are det checking, so can push that little bit harder (to the point of det and then pulling back). Expect to pay around twice as much for a live map as to fitting a generic chip.