I have them, about 4200 miles on the headers. I've thrown a "cat system efficiency below threshold" code twice. My car has ACRX headers, single metal substrate cat and stock mufflers.
I normally drive the car with minimal "putting around". Drove it to the VOI from the West coast, to the drags, autocrosses, etc., no codes.
Early last summer I took the car out to just drive it on some country roads about 6 miles out of town. On the way back, I got caught in a freak thunderstorm and drove the car back very slowly to keep the tires from throwing up crap all over the just detailed wheels, suspension, etc. Just before home, I threw the code.
On a VCA run to Santa Cruz this summer, tons of slow driving with the wife in the car, driving in stop and go traffic, etc, threw the code just before home after about 5 hours of very mild driving and low revs.
Both codes were thrown in the last 1000 miles of driving. I suspect that aftermarket cats lose efficiency (I don't care who's brand they are, they'll never be as reliable as stock) with age. As the cats get older I'm figuring that the system will throw codes more often. My gut is telling me that aftermarket cats may be a "wear" item if you're not running a Mopar controller.
When I drive alone, I drive much sportier (which probably keeps the cats lit and hot) than I do with the wife in the car on a slow cruise event. I've driven the car about 400 miles since the VCA run to Santa Cruz with no codes.
Cheers,
George