You want quality and you went to eBay? What were you thinking?
Sorry, that was mean.
But really, Mountain has a very similar driver. If you are ordering from them anyway (which I would for the LED), it will cost you the same and arrive much faster. It might even come from the same source, but I would trust Mountain's quality control before some random seller on eBay. They have a great reputation.
For high quality I would probably look at the b3flex from taskled.com.
Also some of the LuxDrive BuckPuck products would be good, and come in adjustable versions. They only go to 1A though, so you might be a bit shy on the output you want unless you use 2 of them and 2 LEDs (see below).
The LED you chose is a fine choice, and the Noctigon MCPCBs are top of the line. If I were concerned about efficiency, I would think about paying a bit more for the XPL instead of the XP-G, as I think it's efficacy is considerably higher, especially at comparable drive levels. I don't know if that's a concern for you, but might be worth thinking about.
When you say 500 lm, are you talking At The Emitter or OTF (out the front)? The difference is how much light is lost in the optics and packaging of your light. It's quite common to lose 20-40% of the emitter lumens to reflector and/or lens losses, mounting rings, etc. Less than 10% is pretty difficult to achieve. ATE lumens are a much more commonly exaggerated starting point than OTF, except among serious flashaholics.
500 lm ATE is probably achievable with XPL at 1A drive current, but just barely. 500 lm OTF will be almost impossible to achieve at 1A with any LED available today. On the other hand, at 2A drive current, 500 lm OTF should be easily achievable with XPL or any other modern, high efficacy LED. If you want to split the hairs between, keep talking.
Other things you might want to consider if doing long rides at night are color temperature and CRI. These can affect both visual acuity and fatigue.
For what it's worth, a few years back we got a microscope at work that had a very expensive fiber-optic coupled light. A large box with high-power incandescent lamp, noisy fan, etc, coupled by a heavy fiber optic cable to a ring around the microscope lens. Think large, like several inches diameter, several inches from the object, to allow room for hands and tools to work on the object being watched. The fellow using it didn't like the light and asked me if I could provide something better. I turned an aluminum ring, added 9 LEDs (probably XP-G2 at that time) on Noctigon MCPCBs from Mountain, some cheap lenses, and a BuckPuck 1A driver (3S3P, for 0-333 mA/LED). Now it's some years later and we've added a second microscope. The new operator hates the old hand-me-down fiber-optic light and wants me to build another LED light. We are looking at adding several more operators over the next year, and I don't plan on changing the design.
