I need more electrodes for my TENS unit and am wondering about people's experiences with different brands. There are foam pads that cost a little more - are they worth it? I use them on my lumbar region and want something that'll stick well and for many times if I'm sweating on the heating pad. I found few reviews on the web - the Dura-Stick II seem to have a good reputation. What about the PALS foam, Valtrode or Uni-patch brands? Thanks.