I know of dealers that would do a custom fit on new cars so they would know when they spotted them on the street or trade in if it was originally sold by them. All at a glance.
I quite like the centre mount antenna, much better then the guard option that got snapped off when the first d*ckhead came along. Made the car look better balanced also.
I need to fit an aerial to mine and I'm still contemplating my options. Centre mount, pillar mount or internal.