The main thing with expression pedals is throw... How many degrees does the pedal go through from top to bottom?
If you are a Hammond player of old, the more, the better! But if you are a guitarist as well, and are used to the much shorter throw guitar pedals, sometimes things like the Yamaha FC7 can seem awkward.
Generally, the curve or slope of the pedal's potentiometer can be adjusted in modern VSTi's to suit, but when putting them into arrangers, it is usually far less customizable. I have several pedals, depending on need. Roland EV5 and EV7, a Yamaha FC7 and a Behringer (mind you, haven't seen that in a while, it might have got relegated to the garage!). Pedals are a bit like keybeds... certain ones are best for one sort of thing, others for something else...
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An arranger is just a tool. What matters is what you build with it..!