any recovered cooling system is closed actully, the 1's with the vent/ overflow tube generally hold less ( hence the reason for the overflow tube ) and fit in smaller spaces, but ither recovery tank, open or closed will still fill the radiator back up as the engine cools with the correct radiator cap ( must have vacuum valve on the bottom ).. a catch can works diffrently, as there is no tube that leads to the bottom of the can, so it only catches fluid. you would have to continually drain the excess out and is not practical for street use