I used this one and it was very good. Nature's Gate sells them for £42 at the moment I saw and they rent them for £26 here. I bought mine and sold it on ebay afterwards.
The first time round I had pethidine, gas and air and this TENs machine which was neither use nor ornament, and was still in agony. The second time, after a recommendation from a friend I bought the good TENs and I managed with just paracetamol and the TENS machine.
Sorry, just realised that it looks like I'm on a commission or something, I'm really not, but it was bloody good!