A couple years ago, some hobbyists here in town sat down with all their test kits and some water samples, and cross-tested everything with every kit.
We were interested in how different kits compare to each other. The results were kind of surprising. More expensive or more steps does not always mean more accurate.
http://rowelab.com/fish/Test%20Kit%20Analysis.pdfWith new kits out on the market, like the Red Sea Master kit, and the Hanna line of electronic checkers, we thought a repeat might be good. This time around, we met up at a local fish store, and we all tested one sample from one tank.
Again, the result seems to be, pick a name brand kit and stick with it.
http://rowelab.com/fish/misc/test_kits2.pdf