I bought two 4x1 switches and stacked them on top of each other.

One was connected to my keyboard and (up to) 4 machines.

The other was connected to my mouse and (up to) 4 machines.

for each machine, I need 2 cables from 2 usb ports on the machine to the switches (one for keyboard, one for mouse)

there no multiplexing, there is no hub, there is just a dedicated cable for each device. It works well though it is a little clunky to throw the mechanical switches.

I don't use the usb ports on the monitor.