The nicest carbon fiber trunk spoiler is the BMW OEM F82 M4 coupe spoiler with a nice break in the middle, that aligns with the crease in the cf roof. The F80 spoiler is different and more e90 like. Aftermarket vendors like RW Carbon and Mode Carbon make an F80 version of the F82 spoiler.
I think the key might be to add a CF diffuser to make the rear look complete.
There is a new F82 M4 CS cf spoiler from BMW that I think IND sells. Saw one in person yesterday on an M4 CS and it is OK. Has the M4=style break, but doesnt flow over the trunk edge like the OEM M4-style spoiler.
Turner has a new e90 M3 cf spoiler. BMW OEM e90 cf spoiler isn't that cool.
https://www.turnermotorsport.com/p-5...t-lip-spoiler/
Mashimoto did a comparison of e90 cf spoiler options. It includes the F82 M4-style and a whale tail option for an e90. Might be from ebay/Amazon.
Cheers