Heard about Hanna a while back from Mr.saltwater. Just upgraded from a 90 gal to a 125 gal mix reef, used up all the old KH test, also have a little money left (got a good deal on AI lighting). So I bought my first 2 Hanna (cal and kh) from BRS along with some rocks and probes. Super impressed after first use. Can't go wrong with a straight up number. Results are much much more accurate that I no longer have to count on my eyes to do color matching under different lighting.
Totally recommend Hanna and planning to replace all my other test kit with their products.