What is it?

It's a converter to put your HPIB/GPIB (or UART/RS-232/Serial port ) instrument on the Ethernet that can be accessed remotely.

It's made by HP/Agilent/Keysight which makes it fully compatible with current software (like the free Agilent/Keysight IO suite, NI-VISA, Labview and MATLAB just to name a few).

If you choose Prologix converters, make sure you check if they're compatible with the 3 major vendor's framework (Agilent/Keysight, NI, Tektronix) since most of the old ones don't (they just serve as a UART/Serial/RS-232 terminal relay. Windows doesn't think of them as genuine GPIB devices)

What makes it special?

Why spend $500 to buy a USB to GPIB converter when you can have a Ethernet to GPIB converter that will be backward compatible with any hardware and OS independent?