6 wk Vs 4 wk laser hair removal?

Is there a difference? Which one works better? I ask because I'm getting lasered at two different places. The underarm is done every 6 weeks with the zapping gun they use at body image I think. The Brazilian is done with one that looks like an ultrasound, no zapping every 4 weeks. I've seen dramatic difference but the underarms it's taking longer as it's every 6 weeks. Began them at the same time. Discuss any difference about choosing 6 or 4 weeks.