I've drilled all 3 of the major ones (Griploc, Switchgrip and IT). Started with Griplocs about 5 years ago and still are doing a few. Simple to install using a standard 1 3/8" slug. What I found sometimes was if I went a little too deep when drilling for the sleeve and maybe didn't use enough glue, then the sleeve sometimes would sink but it only happened to one of my friends who has a high backswing. Tried Turbo Switchgrips a couple years ago for me and my friend because you could get an inner sleeve with no slug installed so I could glue our custom thumb molds into it. Those are fine and we never had anything go wrong with them. Just you needed a 1 1/2" bit to install them so there is an expense in that. Finally just started installing the ITs just about a year ago. Surprised we got the kit as its pretty expensive, but oh well. Once I got the hang of installing them, I can install one in about 15 minutes. Very well made and I have only had one malfunction and that was because the glue failed between the slug and the slug it. My most recent issue was with that some ITs were hard to turn for customers with extreme pitches, 3/8ths reverse, 5/16th left etc. I have been told it is because when you switch to the 1/2" bit and drill for the ball IT, then sometimes if you go fast then the bit may wander and the two holes will not be concentric with each other causing the slug to bind. I remedied this by starting to drill with the IT bit, going only about a 1/2" into the ball, then switching to the 1/2" bit and drilling it all the way, then switching back to the IT bit and finish drilling the hole. Its the reverse of how you normally do it, but it works for me and its mostly because our drill press doesn't have enough stroke to reach the required depth without re-chuking the bit lower in the chuck. But in my opinion the ITs are the best.
Hope that helps.
Jarrett Roseboom
Ebonite fan
pics of my equipment
http://s638.photobucket.com/albums/uu109/jarrettcr/My%20Bowling%20Equipment/
