You are right about the fan pulling air through the Mac. On this model of Kensington System Saver there is only one switch. The Mac Plus is plugged in the System Savers plug in as is the external hardrive. The system saver has a nice long cable to plug into the wall plug in. Leaving the Mac Plus power switch on all the time, allows you to use the front mounted Kensington power button to start both the Mac Plus and the external hardrive together. When I get some time I might drop a newer hardrive into the Rodime Plus 20 external hardrive case.