your mum must not have been using it right caus they are effective when used properly
I had a 56 hour labour with ds and put mine on and it was a lifesaver i must have worn it for 20hours or so and when i took it off to get in the pool the first contraction i had baiscly knocked me over as id been walking or bouncing through them till then and i was 7cm dilated.
Many reccomend the specific labour tens machines you can get from Lloyds pharmacys and boots they have their own brand ones or the Mama Tens , mines just a basic one i got off ebay thats suitable for use in labour but doesnt come with a specific "contraction./boost" button you have to turn the intensity dial up during the contraction instead, i have to get new gel pads for mine as i dont think my old ones are still sticky enough,
theres lots of options out there, mine is most similar to the babycare femme Tens unit with the booster button removed, ive already got it out and ready with fresh batteries i just need the new pads and i'll be ready to go when labour starts