Not bad
My Staffie is 3 years old, and we have tried dozens of KONG products. The ball, the frisbee, and everything in between. Basically the whole Extreme range.
The most resistant has been the ball, although it only lasts for a few hours. The others are too lightweight and finicky, they don't even make it past five minutes. I'm not sure KONG should be marketing these as 'indestructible', and while they're at it they should think about the price because with this kind of durability it's poor value for money for the customer.