There’s no such thing as an ethernet cable splitter. If the cable is actually running ethernet on it, you need to use a switch. That product is a cat-5/RJ-45 splitter, but it will break badly if both devices connected to it are turned on at the same time.
You can get a real switch for $10: https://www.amazon.com/TP-LINK-5-Port-Ethernet-Desktop-TL-SF1005D/dp/B000FNFSPY
Or spend a little more and get gigabit: https://www.amazon.com/TP-LINK-Gigabit-Ethernet-Desktop-TL-SG105/dp/B00A128S24