Best changeable thumb product out there. Great for players that have swelling issues when they bowl frequently, trouble with a consistent fit and for people that drill a lot of balls.
In the past where I have bowled for consecutive days, my thumb swells and I have to open the thumb holes, then when I get back to regular bowling it doesn't fit, the IT prevents this from happening. Just carry multiple sizes, I have 6.
Another plus, if you make a mistake in the fitting or working out the thumb hole, you just throw it away and start over, you don't have to reslug.
If you drill a new ball, you don't have to work out the thumb, just glue the grips, put in the IT thumb and off you go, perfect "feel" every time.