Help w/ Furutech e-TP80e AC power line receptacle

Hi y'all,

Just bought a Furutech e-TP80e used. It has 4 filtrated plugs for digital devices, and 4 non-filtrated for amp, pre-amp and everything analog, if I understood correctly.
It also has a small metal tip called "polarity check" with a red LED. I guess it helps to find where the "line" is vs the "neutral". But actually when I point my finger on the metal tip, nothing happens, even if I turn the device's plug on upside down...
Did I miss something? Or is it the tester that doesn't work?
Maybe I have to acknowledge that here in France, the AC power outlets are single-phase with Phase, Neutral and Earth.
Some people here are claiming that inverting the way you plug our device (i.e. inverting phase and neutral) may have an audible impact on the sound. After having tested that, I must admit I haven't noticed any difference, I'm afraid...

 

Please read the new thread below. Your comments and knowledge of European power would be appreciated.

A new one on me

 

Please disregard the above. It seems I don't know my right from my left. Been that way all my life.