Well, the moment you've all (not) been waiting for...
(Sorry this is so brief, I'm a bit pushed for time)
The box:
Canon lead top, Ebay lead bottom.
The Camera-end of the Canon connector:
The Camera-end of the Ebay connector:
It definitely looks and feels cheaper, although fits well on both the camera and the flash without any movement.
Cable is a bit thinner so puts up less resistance when stretched, but may also be a bit more prone to damage/wear.
Canon lead has a locking "switch", where the Ebay one just has a twisty dial to clamp down on the camera.
The Canon has metal brackets on both ends, while the Ebay jobbie has a metal bracket on the flash end, but a plastic clip on the camera end, which will probably wear down on the camera's hotshoe bracket over time. Also note the pins that connect to the hotshow on the camera are more pointed than the round ones of the Canon - this too could cause more wear on the camera's hotshoe.
Alright for £20 I guess, and fine for what I need it for, but you do definitely get a lot more for your money with the build quality of the OC-E3.