ISUK:

It covers all the areas of the car that are very vulnerable to stone chips in shiny gloss black paint which shows up every mark, scratch and stone chip far more than the regular plastic finish does.

it's only really the front diffuser, isn't it?

side air intakes are higher up, quite far away from the front wheels,

mirror supports are higher up but nearer the front wheels,

roll bars barely ever get chipped,

rear diffuser away from line of sight of rear wheels.

Doesn't your Cayman GTS have the GTS exterior black package?