So what is the difference?

[WindowMaker]

So I look at something like this

http://www.reefshops.com/sunsun-jvp-102b-wave-maker-vibration-pump.html

I see a Hydor pump (oh look, they even mention it in the description). I understand that some people will feel that this is probably some knockoff. But the reality is that most of the time the "knockoff" is coming from the same factory.

Any opinions on what the worst that could happen is?

[toytech]

Its probably exactly the same , its just an unlicenced knock off . It will probably work fine but your buying from a company that has no reputation or might not have anykind of waranty . Also your supporting a company that didnt design the product , or spend anytime developing it they just happen to be in a country that dosent have any copyright laws thanks to a biased government .

[WindowMaker]

Its actually quite funny. I have a friend who owns a fairly large company that has parts made in china. When the economy went to crap he lowered his order quantities. Shortly after that, grey market versions of his product started popping up. It appears that if you dont pay the factory someone else will :S