Did Exotics Tuning give any explanation or just a refund? I have to agree with
ILSMKU, I even had a bad fitment experience with Challange. I purchased a diffuser from another member... Never installed. I couldn't get the back end flush with the bumper. You could always see a slight gap and it didn't want to force it. Took the piece to two body shops and they couldn't offer much help or suggestions.
After seeing mode carbon parts in person I would recommend them. Any other carbon parts will be BMW performance.