Other thing is, if you are going to get a knock-off,
fasttech sells them for 5 bucks plus change, free shipping. Which is probably where this eBay vendor got his stock from. Might as well get one from FastTech if that's what you want.
One major difference (that you may or may not care about) is that the knock-off from FastTech says it is an acrylic tank, vs pyrex (Kanger). Acrylic is stronger than glass (i.e. less liable to break all else being equal in terms of thickness of the tank) while also being lighter. However, acrylic is easily scratched and is also flammable, while pyrex of course is not. (Scratches
can be buffed out of acrylic.)
Otherwise I don't know how the knock-offs perform vs the real thing, as I only have a Kanger. Since they use the same heads the only difference might be the draw, assuming the seals and specs are otherwise the same. For $5 it might be a good extra tank, but I'm sticking with pyrex tanks, personally.