The tests are not electronic. these are small portable colorimeters probably each tuned to the narrow wavelengths of the particular test they do. So it is just a replacement for our test tube tests. but in the case of things like phosphate, nitrates etc. wher you are trying to match a colour these are most likely more accurate as they don't depend on the colour temperature of the lighting you are doing the test under and a judgement call of what you think the colour is etc.
For stuff like Alk and Ca and Mg that are titration tests with a distinct colour change the advantage might lie in greater precision (which we'll know once they release more information about the checkers) and convenience.
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