Okay - Does anyone know what the rear diffuser is??

I've seen so many photos of the RDX, but I can't tell where the diffuser is or what it looks like.

What purpose does it serve??

Is it worth the money?? The front spoiler sure is!!

 

its that grey piece that u see in the discription picture... it says it just adds a "lowered" look to it... just like the front, i dont think its worth the money, but im getting it anyway