At the moment, if you change the head unit you will lose your steering wheel remote controls and the CANBUS security check (which is no great loss). The FF head unit is specifically made for the 147 and uses the CANBUS to check the match between the car and head unit. This means that your head unit will not work in another car but you CAN fit another head unit (using a facia adaptor plate, £5 from your dealer) to your car. As I said the remote controls which use the CANBUS to send and receive information will not work, but nothing else should be effected. It will not effect your dashboard, dials, indicators etc.
The obvious advantage is that you can get a better head unit with MP3 and DAB capabilities.
In the future this situation may change and Blaupunkt, Alpine, Sony etc may release some CANBUS capable after market units but there are none available at the moment and nobody has any idea of plans, release dates etc.
So, the choice is yours. Stay the same and wait or get better sounds and facilities now with redundant steering wheel controls.