I have a very simple question regarding what resistor to use
Ebay specs are unreliable, and usually non-existent.

The Bridgelux 10W chip comes with no heatsink and requires a big one.


It is actually made from 9 chips in an array of 3x3 or 3S3P.
Thus you need more than 9V and >=1.2A
If using say a PC PSU at 12V with a 3V drop per 10W ~9V chip then 4V/1.11A= 3.6 Ohm 5W resistor 
This needs a well regulated 12V supply and AWG 16 -18 wires for a short distance(3m)


Tolerance error on Vf of LEDs depends on quality at 10W. They are usually binned in 0.1V increments and these may be rejects at Vf>10V Then use Jonk's calculations for 2V drop with   1A or 2 Ohm   

The exact answer may be around this. But you are better off focusing on a heatsink design  like a CPU cooler. (est)
10W High Power LED PCB Grow light Aquarium Heatsink White Certification


after doing some research on Bridgelux's website and their distributor , it seems the 3x3 chips here are obsolete and replaced with higher voltage arrays in their 3rd and 4th chips ,which favour lower cable loss.  SO these chips are cheap for a reason. Good ruck.