The “VESA DisplayPort Alt Mode for USB Type-C Standard Feature Summary” pdf document describes a USB-C to DisplayPort cable that is bi-directional.
The Amazon product page says the USBC-DP is not bi-directional. The Plugable product page is not as clear and only says that the USBC-DP supports DisplayPort displays.
There are some USB-C displays that a bi-directional cable might be useful for (those that don’t use USB-C for power, as DisplayPort only has 1.65W). Future Thunderbolt 3 Displays using a Titan Ridge controller will be able to receive DisplayPort input through their Thunderbolt 3 port.
So why did you choose to make a cable that is not bi-directional? What is the difference in hardware and price?
Moshi seems to have the only bi-directional USB-C to DisplayPort cable and it supports DisplayPort 1.4 and it’s twice as expensive (but I don’t know if that’s because of the DisplayPort 1.4 capability, or the bidirectional capability, or the VESA certification).