The dongle plugs into a USB port on your computer so you can activate the LiveView feature with your tethered Valeo and Aptus backs. The computer screen will display what the lens sees in real time in B+W.
They are required for Leaf Valeo and Aptus backs.
I sold one in 2008 for USD1,170.
I suggest a price of USD300 plus freight plus fund transfer charges.
Roger