We have been selling Switch Grips in our shop for about a year now, and they seem to be holding up quite well.
I wasn't ready to retrofit every ball I owned, and I wasn't drilling any new equipment, due to a possible ball contract, so I didn't bother with them at first. Eventually, the shop owner told me that we needed to make me an inner sleeve, so I could throw try his stuff now and then (his span and fingers are close in size to mine).
Once the ball contract was no longer an issue, and I started drilling new balls again, I have been putting them in every new ball I drill. In addition, I put one in a previously drilled ball on which I had really done a bad job of working out the thumb, resulting in a ball that didn't feel at all like the rest. That gives me a total of four balls with switch grips in them so far.
I don't use a Switch Grip in my spare ball. I just make sure that I get the thumb hole right in that one. That way, I don't have to be switching every time I don't strike, which, of course, is more often than I'd like.
I don't have the same issues as some folks, where my thumb changes size often. As a result, I have not yet made a second inner sleeve. I just make size adjustments with tape, as required.
The only mechanical issue I've had with mine was when I was trying the shop owner's Ebonite Xcel Particle, my inner sleeve was difficult to get in and out. I have seen occasional problems with other customers. It seems that Storm and Ebonite balls give us more problems than others. It must be something about their cores. If we don't work out the hole extensively after drilling, especially down near the bottom of the hole, the inner sleeve is difficult or impossible to get in/out. We had one case where one of the guys was trying one of the shop owner's balls and his inner sleeve got stuck. They ended up having to drill it out because it was stuck so badly.
I personally don't have any more trouble getting the outer sleeves out of balls for plugging/redrilling than some slugs or thumb inserts. In the rare case where it becomes difficult, I just drill it out. I've only had to do that once. We haven't had any problem reselling plugged balls that had Switch Grips in them.
As for getting the proper depth of the hole, we have found a virtually foolproof way to do it - so much so that I can't even screw it up.
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RW (THB)