I ordered these last night and they arrived this afternoon. So far, so good - on the TV over Ethernet I am getting 100% of the speed I’m seeing on 5GHz WiFi on the iPad, which is a win as previously the TV was on 2.4GHz and getting little more than 10% of what was available. I can’t report absolute speeds at present as the home network is being quite heavily used, as is our local 4g cell. I should be able to identify the best throughout I can get from powerline in my home first thing tomorrow morning (or maybe late tonight).
It does work, after a fashion, on the socket ring in the dining room which is on a secondary consumer board but it’s weak. I’m getting much better results from putting the second adapter in the kitchen, which is on our main consumer board. End result, the iMac in the dining room is connecting via 2.4GHz to the plug through the wall, less than a metre away, and getting a good, stable connection.
So thanks everyone for your help