This device has four ports, yes - but one port is designed to switch/select between the other three ports. And yes, HDMI has a two-way component, so if you hooked two of these up back-to-back you could connect any one of three sources to any one of three displays.
No, I was wrong.
If you zoom in on the graphics, they clarify there are FOUR input ports (one is on the front) and one output port. The text is slightly confused about that, but a picture is worth more than a thousand confusions.
The amazon page is the exact opposite. Title says 4 devices; features say 3 devices.
The text/copy is MUCH more likely to be wrong than the graphics - and the graphics got specific about Port One is on the front, Ports Two thru Four are on the back, AND the shared-output port is on the back far-left (so “4+1” does match having FIVE total HDMI ports on the device).
Luckily we have these forums to deal with the occasionally-correct info-surprise and the normal “say what?” befuddlement…