This product is what is known as a "LAN galvanic isolator".
I recognize it because my wife is a heart surgeon who does ablations (for tachycardia and things like that) when peoples' heart beat is off. They need all the stray electric signals isolated.
You can buy much nicer ones, that have a proper ground (for serious surges) for $31.59 on Amazon. Or one that is the same for $13.99.