I just got a glossy spoiler for my M3 (Amazon, Tslaucay) - to me the matte doesn't show off the carbon fiber nearly as much. Pretty sure all of the OEM spoilers are matte. Also, get real carbon fiber - it's not that much more expensive and well worth it.
Basic install is fairly easy, but I had some gap issues. After watching tons of videos I don't think people are showing how difficult it is to install a spoiler with no gaps. In every video that showed the spoilers in detail I could see gaps or they didn't show detail. I am working on a video of my install and how to eliminate the gaps after install using black RTV. Using RTV to seal the gaps is more difficult than installing the spoiler, IMO.