Yep I had one & it's the only pain relief I used for the 22 hour labour!! Cannot recommend one enough
I really liked having something to focus on - pushing the button. Towards the end it didn't make much of a difference (I thought) but DH told me after that the pads had started to slide off their designated marks. That's one thing I have to say: use duct tape to tape them down as your back does get quite sweaty during labour. My DH insisted on doing this & I was quite annoyed at him but am really glad he did!!