I recieved my retractable ethernet cable and tested it with a cheap cable tester, it seemed fine. I hooked it up to my laptop and switch, worked. For fun i hooked it up to my employers fluke cable tester. It seemed fine but halfway during testing errors showed up. The Fluke tester reported the cable generated too much line noise.
my conclusion, nice to have in your bag for troubleshooting, but remember it might cause problems of its own.