No difference. The pedal on a multi-effects system is known as an "expression pedal" because it can be assigned/programmed to control more than 1 effect on the system.
For eg, you program your multi-effects processor to have a reverb and a wah effect both in the chain. You can assign the expression pedal to the wah-effect, so that it becomes a wah-pedal, or you can assign it to control the reverb, in which case you could call it a "reverb-pedal".
any multi-effect processor which offers wah as an effect and has an expression pedal can work as a wah-pedal.
My gear, currently up for sale
Washburn X-16 anarchy - SOLD!!
duncan pickups - I wonder why Im selling these.