From what I've read, this is a pure "plug & play" setup with no wire splicing into the car's harness.
I think there are two wires that connect to the battery, then you plug the car's fog light sockets into the new harness, then you plug the harness connectors into the back of the bulbs. The only "fabrication" is finding a place to mount the relays. Looks like a very simple install.
In operation, when the relays sense the fog light switch has been turned on, they close allowing juice to flow directly from the battery to the lights on thicker wires (i.e. less resistance), giving more juice to the bulbs, which will allow them to burn brighter. Since the wiring is "thicker" (smaller gauge), you can also run a higher wattage bulb than you can with the car's "stock" wiring without worrying if that might overheat the wiring. The end result is getting brighter fog lights while running halogen bulbs. Since you're still running halogen bulbs, you don't have to worry about light scatter like you might have with LED or HID bulbs, because the OEM fog light housing was designed for halogens.
I like the concept, and I think this is probably the direction I'll go...