Copper kits are useful if you use or have used an ionizer or copper based algaecides, if your heater went south and the corroded core was copper and might have dumped copper in the water, if you use well water that might have high levels of copper, or if people's hair and/or the entire pool (not the water) is turning green.

If you only need one test (you stopped using the ionizer or you don't know what that stuff you put in the pool a couple of years ago was, etc...) and you trust a local pool company, it would be cheaper to have them perform the copper test. If it comes out OK, than there is no need to buy a kit.