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The lip is made for downforce, hence the stepped type lip. The sides (if I remember correct from owning a S2k) is made with a slight raise on the rear (in the design) to give it sorta a side diffusor feeling, the rear looks nasty but it serves it's purpose as well, downforce.
ChargeSpeed is known for their functioning parts, not only for looks... I also agree with most, it'll look better either painted or on a dark colored vehicle.