The Pantera Electronics fan controller uses Pulse Width Modulation to control the speed of the fans in proportion to coolant temp. With this system, your fans will run at a slower speed most of the time, than they would with a switch or switches. This is both quieter and easier on the fans. Also, if you have your fans mounted in a shroud, unless there's a baffle that separates the two fans, you shouldn't have the fans turn on at different temperatures. If they do, when one fan is on and the other is off, the one that's on will draw air through the other fan's opening in the shroud, rather than through the radiator. In such a case, the fans only pull air through the rad when both are on.