On Sun, 20 May 2018 21:26:36 +0100, Jim wrote:

What's the advantage over a £20 tone tester pair?

A £20 tone tester pair senders don't like being connected to the
mains. Even if it did I'm not sure how well it would work as all they
do is inject an audio tone onto the pairs. On live mains the 50 Hz at
+48 dBV swamps my ordianry tone tracer probe. Reading between the
lines of the description/manuaI for the Soocket and See kit I have a
suspicion they may be RF based.

--
Cheers
Dave.