The cores are closer to each other than to the outside world so it is less affected by being strapped to a mast or clipped to a brick wall than coax is. In a low noise location the 21metre length picks up 2 S-points less noise than coax or 300R twin. In a high noise location this can be 4 S-points less than coax or 300R twin. Twin feeder loss is about the same as RG58, which is less than 2dB for 21 metres at 30MHz.Used with a properly balanced horizontal or inverted-V dipole it is so quiet compared with a coax fed dipole that the first impression is that the aerial and feeder is somehow faulty. That is until you tune around and find the stations are there at the expected strength but against a much quieter background. The twin feeder works fine with monoband dipole or multiband trap dipoles.
It has two polyethylene sheathed cores within an oval solid polyethylene outer moulding. It does not allow water ingress so will last for many decades without degradation (unlike coax). Any unused feeder is not to be chopped off but just coiled up and hidden out of sight in the shack.
As it emits an insignificant electromagnetic field it doesn't fill the shack with radiation. The feeder needs the full length to act as a common mode balun in its own right.
The item "Antenna Centrepiece, 20m 95 ohm low TVI low noise twin feeder, & 11 Balun" is in sale since Tuesday, October 3, 2017. This item is in the category "Mobile Phones & Communication\Radio Communication Equipment\Antennas\Ham/Amateur Radio Antennas". The seller is "spectrumcomms" and is located in Dorchester. This item can be shipped worldwide.