I used a TENS and I think it helped a bit. I had contractions on top of each other and I liked to turn it up high when one was was finishing and the other was brewing. I couldnt bear it on high at the height of my contraction though, as it was just too much, and I needed all my concentration to deal with the pain rather than the pulses of the TENS.
Also, I held out on using it for the first 24 hours cos I thought the longer I left it, the better chance I had of getting max effect. Not the case! So I would recommend you use it quite low for early labour and then boost it up when you need it later.
It is definitely worth a try. Hope this helps. x