I used Roland pedal with my Hammond SK-1 before, because of the irrationally high price of the EXP50. It was however noticeably unable to express fine details and the total travel of the pedal was short. Also, I had problems with the amplification preselection of the Roland pedal - was very hard to set the knob right (tenths of millimeters of turning the knob!), and has always moved from there over time.
With this pedal no pre-adjustment is needed, just works fine (naturally) with the Hammond, and I finally learned how much expression the pedal can add to my organ music while the predecessor was rather a loudness control than an "expression" pedal.
Rather expensive, but essential, and very satisfying. Highly recommended.