I resisted getting Switch Grips for years, because of the failures I had heard about. I finally broke down and got them. I was told also, the contruction was much better now. Now that I have them, I could never go back to bowling without them. I found the biggest difference was in my Spare ball. I throw straight w/ Plastic at almost every spare. Started that when bowling some PBA regionals and some sport pattern leagues. Having that same feel in my Spare ball is immeasurable.
But, with that, I do have a small warning. Make sure you go to a reputable shop, as others have stated, most failures today trace back to improper set-up. The other thing to watch for is if you are planning on moving. I have moved around quite a bit for my job. In my last relocation, I ran into a problem. The driller I went to, who was recommended to me by a an old friend, said he could drill my ball with switch grips. But is drillbit was set at a different depth than my previous driller's was (or maybe one was sharper, there are a number of reasons why this might occur) even though they are supposed to be standard. But, since I was a "new" customer, he didn't want to change the depth of his drillbit,because then he might not be able to get it back to where it was for all his oid customers who he has drilled for in the past. He made me a new thumb slug, but the feel just isn't the same as my other one, so the ball is useless to me at this point. I haven't had the time to go to another driller and get them to correct it yet. So just be aware that this might be an issue as well. But overall, I don't think you can go wrong with either the IT or Switch Grips, and you will love it once you make the change, I think.