These TENS machines were all the rage in the '90s for labour pains. I was given the use of one when I had my second child. To be honest, a warm bath was more soothing at the early stage than the machine was for me. That is just me, though, we are all different and each pregnancy/labour is different.
Many years later I was loaned a TENS for muscular pain and found it more annoying than soothing. If you can scrounge the loan of one it may give you an idea. Good luck.