Time to stick my oar in and get a mouthful
I'd say there main aspects to this are price/ethics and quality/reliability.
Price & Ethics
The main benefit of paying less for this in China is mainly due to, in my opinion, child labour and/or environmental disregard (churning out polluted water/air) this is the ethics dilemma, by buying from the far east you are improving the eastern economy at the cost of European jobs and supporting communism.
Quality & Reliability
I think pretty much any developed country has access to aluminium billet and CNC machines. The aluminium and plastic quality will be down to the design and specification, neither of which you will know. There is also the design, which may have been tested on a functional basis, but possibly not on a durability basis.
Conclusion
By buying a cheap third party unit you risk premature failure, design weakness and/or lack of process control/QA, by buying a higher quality (possibly european) part you will most likely have the benefit (read beaurocracy) of more testing and quality control but at a monetary cost. The chinese and/or Japanese parts may be perfectly functional and fulfil your needs but you'll only be able to tell by rolling the dice and seeing how they last. Of course on ebay you could also buy a set of Yamaha levers to find that they were copies of the higher quality items anyway.
Of course the specification and the design could have been done in the USA or UK and they just produce them, but how would you know ?
Don't get me wrong, China creates a lot of very high quality parts and can do so cheaply, but the cheapness is unethical :-)..... (now I'm off to ebay to buy some cheap knock off Chinese levers)
