These are becoming increasingly popular as an after market accessory. Want that BM look?  There appear to be four catogaries.  1. Replacement origional equipement. 2.Functional fin base replacement  3. Functional aero Fin covers. 4. Fake imitation.  What has to be considered is will the new aerial be good reception? we recommend those with a power boost lead included of the functional screw on base.  Secondly can I remove the headlining to fit?  If the answer is no, then we recommend the new alloy or plastic functional cover style. See pic.

 These stick over origional base and earth onto origional anntena.  These are best secured with clear or body styling adhesive.  Last but not least are the stick on immitatiion style.  For further info and products check out speedwithdesign.com