Master I
I climbed on the Master II for a couple seasons. For the most part it suited my style, but because the attachment point is high, it loaded around my waist alot. By the end of my 2nd season in it, when I was done a climb, and slacked off the waist belt, the pressure relief would just about put me to my knees in pain. I think it was placing alot of prssure on my kidneys and lower ribs.
The Pro series Master gives alot more versatility, and a friend is quite pleased with his.