I used it with all four of my labours and found it helpful each time, especially as something to focus on - I think that was as important as the pain relief.

With DD2 I was stuck on the bed for my whole labour, I got through it almost all the way without it and used gas for the last three or four contractions before she finally engaged. I didn't find it great then for pain relief but it was distracting.
What I really wanted to do was move around, I think if I had been able to move around I would have done without the gas (in that instance).