Feintech VMR00100 HDMI 2.0 Repeater Signal Amplifier 4K HDR, up to 50 m cable length, white

After a lot of fiddling around trying to get this device to make my 4k TV work at the end of the HDMI cables built into the wall, I tried the device on the end of a short cable which was working. Adding this device actually stopped it working. Yes, it was connected the right way round with the 5v power supply connected and the green LED on. So this device actually degrades the HDMI signal!

excellent