I think it looks great if done right like Chi123. His is the best custom setup I've seen. The Wald always looks good but its Expensive. Just plan ahead because if you want to get a rear lip it might not fit (like a Vertex or GFX).
This is my buddy David (CL user name Barke) with his Wald rear exhaust and Wald kit.
i did dual custom setup... placed similar to what an ISF looks like... just waiting this week to complete my difuser so you can see a much better picture. u cut the oem bumper in order to fit properly.