I used a mold for the longest time, but since I don't bowl as much anymore my old mold was way too big. I tried redrilling new thumbs and nothing felt right, and I was having problems with swelling and consistency ball to ball so my PSO wanted me to be the guinea pig for trying these out. I put the ultimate sleeves in 6 balls and drilled 3 thumbs. They're simple to install and appear to be very secure, but so far I've had 2 of the thumbs get completely stuck in balls and had to drill one out, one thumb that wouldn't go all the way down and was raised up in the ball. It is near IMPOSSIBLE to switch thumbs or balls without using the switcheroo tool, I've had numerous people try. I'm probably going to go with switch grip this weekend just for the ease of switching alone. I've always been skeptical and hesitant to use any interchangeable system and ultimate's product didn't do much to sway me.