I didn't run mine during the majority of my cycle...read many places not to run it. But, I've also seen some posts where people did run it with no problems. I started mine once the cycle was complete and 1 week before adding my first fish to the tank. That week was a good break in period and all works well now.
But, i did run mine in water/vinegar mixture for several hours before even putting into my sump in order to clean out any manufacturing gunk that could be on the plastics. I think this help it break in fast.