Yes the sound of the Sony radio of your Ebay link will be much better than the standard radio.
In my opinion the Sony looks great but that is a matter of taste.
Note that a Sony radio from a Mondeo MK4 or S-max/Galaxy is not suitable for a Focus MK2.5. The Mondeo MK4 and S-max/Galaxy Sony radio is technically different than the Focus MK2.5 Sony radio. Both radio's look exactly the same but the communication protocol is different. A Mondeo MK4 or S-max/Galaxy Sony radio can not be configured in a Focus MK2.5 and in some cases shows "Unconfigured Mode" on the radio screen.
The Sony radio from a C-max or Kuga is technically identical to the Focus MK2.5 Sony radio. The only difference is the front of the radio. The Focus MK2.5 Sony has an oval shaped front (Island) while the C-max/Kuga Sony has a square front (like the Focus MK2).