Adored mine! I had G&A as well, but it didn't do anything for me and just served to distract me when I needed to turn inward and concentrate on getting through the contraction. My TENS (from Lloyd's pharmacy) was great though. I put it on around 3cm, right before they broke my forewaters (I'd planned a home birth but was in hospital due to my hindwaters breaking at home showing thick meconium). My labour was quite hard due to the waters being broken and the presence of meconium, but I coped very well on the TENS. The only time I "lost it" and thought I needed an epidural was when a stupid doctor examined me and declared that I wasn't as dilated as my previous midwife had said. I think she was wrong anyway, as I delivered soon after; but it really could've put me off track. My labour, from the hindwaters breaking at home to delivery, was under eight hours.
I loved that boost button. Mine had a strap around it, so it was still nearby if I dropped it out of my hand. By the time the midwife took it off me (when I was ready to push), I realised I'd never got it above 6-7. I'd been so distracted and worried by that stupid doctor. I intend to plan a home birth next time around, and I'll be using my TENS again and hopefully won't have anyone messing with my focus.