You can't go wrong with the JGMods rep
It comes in (4) pieces as you stated:
- Bumper Cover (made from OEM material)
- Tow Hook Cover
- Bumper Center Trim Piece (part you spoke of)
The Diffuser and that center trim piece that goes in the recess are natural black plastic finish - some leave them as-is, some paint - I would have painted mine matte black (if I used it), but I got the BMW OEM iS Sport Diffuser to go with the bumper.
For that center trim piece I used a CF Overlay that I cut from Carbon Fiber/Cleared sheet stock with adhesive backing that I got from DragonPlate.com
The center trim piece has alignment posts that match holes in the bumper recess and use 3M double sided tape to attach (included & installed on trim piece)
No need to change out your bumper guides either - the bumper cover is made to use your factory standard bumper cover guides.