Janni I wouldn't be concerned with the pads being reusable - unless you want to go in the bath or shower you'll most likely just leave it on. I thought I'd be in & out of the water but once I got my TENS on that didn't even cross my mind!!
A word of advice - pack some duct tape with the machine!! You do sweat during labour & the pads can move off their target. We told the physio I hired my TENS off that we had used duct tape to keep everything in place & now she includes a roll with the hire.