let argue the other side... i test a lot, ph. Mg, Alk, Calc, Nitrates, and i see i get different results depending on test kits. i've taken my water to some places and they say my nitrates, for example, are much lower than i get, which is usually about 10 (at the store, they told me it was almost at 0). I did this b/c i bought a sailfret test kit from someone here, and when i tested the nitrates, it was off the charts (around 80 ppm), so i rushed to the store to check it out.
It would be great to test my water w/ someone that has the high end testers to see how accurate my readings are. Therefore, i would really benefit from this.