I couldn't stand it really, it just meant there was no relief between contractions for me when it was on and used in the recommended manner. I had a 1 hour plus car journey to hospital during which I wasn't able to move around (my previous way of coping) so ended up switching it on at a low level (literally one of the four lowest levels) during contractions and off in between just so I had something to do as I felt pretty stuck and helpless.
Not being able to cope with more than a low level of TENS (and not at all between contractions) made me fear I wasn't 'managing' pain well at all and I feared I was in early labour.
I gave birth without any form of pain relief within an hour of arriving at hospital and think I had my first 'pushing' contraction whilst still in the car. (I may have been in transition for part of the journey, or the long walk to the ward, it hard to say as my contractions were never regular) So it wasn't that I had a low pain threshold, it was just that TENS was a sensation I couldn't stand! So if you don't get on with it, don't assume you'll need tons of other pain relief, I think its just one of those things that works for some and not others.
I thought it was worth buying it and trying it because I knew I would have the long car journey when there would be few alternatives, and I was going to a CLU rather than my preferred option of a waterbirth at the local MLU. So I wouldn't have water available and I wanted to avoid medicated pain relief if possible, so wanted to have an option in my control!
I don't regret getting it, but I didn't really find it worked for me in terms of pain relief. Just gave me something to do in the car. It might be because my contractions weren't typical or because I have some sensory issues, or maybe DH didn't put them in the right place - who knows?
Good luck!