I realize this is an older thread, sorry.
I had been using the Boss FV 500 series expression pedal because I already had a few, and it worked as expected.
I became interested in the Mission epi-kp, Kemper specific unit, but didn't see a need for the toe switch.
I just purchased a standard Mission epi with spring installed to return to heel down, from their B-stock retail store.
I love it !!! Having the Spring to return to heel down has a great vintage pedal feel.
I have the KPA wah setting to de-activate at heel down, which is perfect for my needs. I have it connected to my Ground Control Pro instead of directly to the KPA. I have tried both ways and haven't noticed any difference worth mentioning.
I also have global settings in the KPA set for wah to volume,( or visa/versa ?), so, any patch that doesn't have a wah active, switches the pedal to control volume, and activate tuner.
The Boss sure took up more space on my pedal board, so switching to the EPI had many benefits for me.
Lots of forum members seem to have the Kemper specific Mission pedal, do you guys see much benefit to having the toe switch?
Maybe I'm missing something.