I'll tell you about my experience with that warranty...
I KNEW my cats were bad before I took it into the dealership. How did I know? The exhaust rattled, so I dropped the ypipe and chunks of the catalyst came out. So I bagged it up. Once I took it the dealership (I didn't show them the stuff) they said the cats were 'fine'. I asked, how can they be fine if I have chunks of them in a baggie? So, I took the chunks in and after about 15 minutes, they agreed to replace the cats. 500 miles later the motor went south due to it being 2 1/2 qts low on oil due to the dealer...yes I should have checked the oil level.
