Expression Pedal?

I recently acquired a Zoom g3x Multi Effects Pedal. This model includes an expression pedal, however it seems difficult to use an expression pedal with theremin so I'm thinking I should return it for the smaller g3 model. The only difference between the two is the expression pedal. Just wanted to get some input on whether or not there is any value in having the expression pedal for theremin so I can make sure returning it for the other model is the right way to go. Thanks so much!

The expression pedal would be for if you wanted to change something during play. I've not used the g3x but typically there are a limited number of effects that you can use the pedal with. If there is some expression pedal function effect you could use to change the timbre during play that could be an interesting capability. I'm actually looking for a way to use an expression pedal to control the threshold for a noise gate for my own reasons

Using the pedal will probably change your pitch field due to the motion of your body. You may want to add vibrato when you use it until you can adapt. Best use would be as a volume pedal so you wouldn't have to drape the wire or worry about overdriving some pedal or amp. With guitar effect distortion the volume of the theremin will greatly effect the sound without the use of a pedal, but most theremin players are not very dynamic when it comes to volume preferring legato and avoiding staccato play. Some will act as a gate for fast attack and decay, which goes into realms seldom taken advantage of.

aliamo: in my opinion only a handful of the default patches for the G3x are useful for theremin.

What you may want to do is
* take an hour or so and go through all hundred patches and try the expression pedal on each of them
* write down the ones you like 
* write down the ones where the expression pedal does something useful.  Then
* collect all the ones you like together so they're easy to access, and
* make some new patches with just the effects that you do like, that use the pedal.