Yes remember them well.
Remember seeing a smoothing iron plugged into one !!!!!
The essential "extra" being rewireable plug in BC lamp base "plugs"
I remember one that had a built in switch for the lamp, so you could leave the light switch turned on to feed the appliance plugged in, and be able to turn the light off if you wanted to. Is that a pull switch on the first picture for that very purpose?
Earthing, or polarity for that matter didn't seem to trouble people back then.
But I'm old enough to remember tv's and radio's rated for 250V ac/dc, meaning they didn't have a transformer, but everything worked directly from the (rectified) mains input.
The other gems I have in my collection are a rewireable 13A plug that has a 13A socket built into it's top, so you could stack as many as you wanted to into a single 13A socket, and a 3 way adapter that converted a 15A round pin plug to three 13A square pin sockets.