Does your friend need a worldwide market to be successful? Might want to consider an approach many large companies take (ie pepsi, coke). Define a smaller test market area where demographics are more easily defined, market the gadget in that area. Compare success in that demographic mix and then extrapolate potential success on a wider playing field. Is this a gadget that will be competing with an existing gadget? If so, then any sales info that can be obtained on that gadget should also be helpful.