The FC$ is like a piano pedal and the FC5 is just a flat tin box affair. I have the FC5. It's half the price of the FC4. You might also want to have the FC7 as well since you can use both at once for the extra functions. Go bananas and get the FC9 stereo pedal as well though if that's the case go for the MFC10 which will do all the functions and more.

Bryan