I used ZGTS because it has high reviews. I've since switched to a dr pen a6. Only used it once so far. Hurt just as much but had more coverage of wounds in less time.
Have you not noticed the ultima a6 pulling out lots of hair when using? that's why i stopped it and switched to a roller, roller doesn't wound as well but seeing clumps of my hair come out after using the pen freaked me out, don't have that problem with a roller.