Spoiler is functional above 130 and does improve downforce. M does not throw on extra body parts for no reason. I know the vents and such but a spoiler to them will have a purpose.
I love the OEM CF one which I have. It is 4 times the size and I have to think at speed it creates a ton of stability and downforce. It has a huge surface area and there is no doubt this provides a big difference in decreasing lift at speed so its a win-win
Plus from the profile view especially, the cf spoiler just makes the car flow right. Kind of like a CSL trunk from the side. Just fits.