Appointment + custom form fields submission

I’m using the custom form fields Addon to add some extra questions to the booking form. The only issue is the checkboxes, which appear to come through in the confirmation email as “1” or just an empty space for “nothing”. Is there any way I can make the “1” Display as a yes and the “nothing” as a no? The best thing would be to have a drop-down, but I couldn’t see this as an option within the add-on.

Any help on this would be much appreciated. Thank you!