I bought a set for my MK3 Mondeo, out of the box and fitted in just over an hour, i paid £20 for a set of 4 sensors with led display\speaker from ******s, the set should have cost £40 but was in half price sale, very simple to install and setup.
I pre- drilled small holes in bumpers even though the kit came with a smallish drill bit, it made it easier.
You wire it in to the lights, so you get power from the reverse light cable, i ran the cabels through the air vent flaps in the boot\rear bumper so i didnt have to take the light out, as, on the MK3 mondeo at least, take the light out, you usally have to seal them back in otherwise you get a water leak in the boot.