Its good to hear the Source Audio Reflex Universal Expression Controller works.
I feel I should mention I bought a Source Audio Dual Expression Pedal and it DID NOT work with my Factor pedals. At both the heel and toe positions the Factor pedals never settled on a parameter value and it was difficult to get all the way to 100 and all the way to 0. The EB Jr. 25kOhm Volume Pedal has worked the best for me. At some point I would like to try the Mission Engineering expression pedals but its not high on the priority list at the moment.