Either, he will cut the plug off the end of the existing wiring loom and join the correct wires to the correct ones on the plug that goes into the stereo. or he has a cheaper place to get hold of the ISO connector.
The ISO kit means you can probably do it yourself and you have the option of refitting the original stereo in the future, if he uses a cheaper sourced ISO connector then no worries, if he cuts the wires then it'll be fine if he does a good job but refitting the original stereo will be a pain.



