What are the signs that show it's time to replace the break calipers?

I have ATE now, but I looked at Fastlane and Bendix are almost half the price, any reason to stay with the ATE?

__________________
1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).