Higher, stronger and I forgot the other one... faster?
If you are doing an aftermarket device install, either integrate it so the operation is completely integral to the rest of the car (like the BT, TV tuner, TV-in-motion, reverse camera, convex mirror, IN-PRO black-outs retrofits), or do it, so it can be removed before the car is sold.
I had an aftermarket system in my '94 530i, that actually drove the price of the car down - so I lost on the value of the car and the value of the system that I could not have taken out for resale or reuse, since I had no original headunit anymore...
Just letting you know about my mistake, so you might be able to avoid it..
Since that incident, I prefer stock only or fully integrated solutions...
Have fun,