I have another solution to the same problem using a monitor which has both HDMI and DVI. The HDMI port is used for the 'main' machine which the DVI is connected

I have another solution to the same problem using a monitor which has both HDMI and DVI. The HDMI port is used for the 'main' machine which the DVI is connected through a DVI-HDMI connector to any secondary machine which I may want to connect. Switching between the two is either automatic - when there is no signal on the DVI input - or through the monitor source selector. The monitor also has a few analog inputs which I have used on occasion with older laptops, extending the scheme even further. Of course this only switches the monitor, not the keyboard so it is not a complete replacement for a KVM switch.