The real issue with fitting derailleur's is that the derailleur hangs down below the rear sprocket, and because the whole chain and sprocket assembly is low to the ground already, there really isn't enough ground clearance or room in the rear of the C5 to fit these - it can be done, but it is quite complex and involved - my C5 has a sturmey 3 spd hub which I fitted myself (first saw it on chas's conversion) which allows me to have a low first gear for starting off, my second gear is the equivalent of direct drive, and to pedal up to about 15 mph in 3rd to assist the motor.
If I hit the 24v button on the flat, the gears are then irrelevant as I just can't pedal that fast comfortably anyway.
I was glad of the gears when I recently went for a long run and completely flattened my batteries and had to pedal back (uphill, phew !!).
Derailleur's will generally give you more gears, but the sturmey hub, while still involving a fair bit of work to fit, is a much easier proposition - that's just my experience anyway.
posted on: 13/11/2013 20:04:45