They worked wonderfully for me for my current pregnancy and my last one. I never had any bruises on my wrists, but I am petite. They did become uncomfortable after a few hours of having them on, so I imagine if your wrists are bigger they would be difficult to wear. The key is to make sure the balls are directly on the pressure point. The brand that I bought at Walgreens...Travel Ease, came with instructions on placement. The few people that I know personally who said they didn't work did not have them placed properly. The ones I got were $10...worth a shot.
Also...just wanted to add: Don't forget that every pregnancy is different. My first 2 pregnancies were miserable, horrible 24 hour/day sickness for months and months...almost the entire pregnancy with my first and the first 5months (whenever I didn't have the wristbands on) with my 2nd. My current pregnancy has been a DREAM. I had 3 weeks of morning sickness in my 2nd month, but then is disappeared as quickly as it came. I have been feeling great for the last 2 months (I'm 19 weeks along). Keep your expectations postitive. Convince yourself that your next pregnancy will be easier. The mind is a very powerful thing and can absolutely effect your reality.