I've been using this KVM switch for a few months now and it has great features especially the mic and audio output switching. However, he has an unpleasant habit. Sometimes he just forgets what it is and what it's related to. During this time, one of the link lights will flash, but none of the four buttons to select either machine will work, and any machines booted up during this time will not "see" the keyboard or mouse. I don't have a standard way to fix it, but if you happen to disconnect and reconnect different keyboard and mouse ports, it syncs back up and works until next time. Note. This only happens when all four computers are idle and then one or more start up.
CKL Quad Monitor HDMI KVM Switch 4 Port 4K@30Hz with Cables - Extended and Mirrored Display Support for Windows, Linux, and Mac
11 Review
NEWCARE HDMI KVM Switch: 4K@60Hz, 2x1 HDMI2.0 Ports + 3X USB KVM Ports - Share 2 Computers on UHD Monitor, with Wireless Keyboard and Mouse Support - USB Disk, Printer, USB Camera Compatible
10 Review
TESmart 1080P 60Hz USB VGA KVM Extender Over Cat5e Cat6 Ethernet Cable - Long Range 984ft/300m (Sender+Receiver)
10 Review
π HDMI 2.0 4 Port KVM Switch with 4K@60Hz, 2K@144Hz,1080P@120Hz Support, 18Gbps Bandwidth, USB 2.0 Keyboard/Mouse/Printer/Monitor/PC Selector, Audio Out/Mic In, HDR10, Dolby Vision, Dolby/DTS, HDCP2.2 Compatibility
10 Review