I received my two types of drop checker from HK recently and have to say that I'm extermely pleased with both of them.
It was fiddly trying to get 4 dKh in distilled water, especially as i was running out of KH reagent but finally did it.
the drop checkers seem decent quality and both look good. My comments on them are that there are no instructions with them and the reagent is from a CO2 tester and doesn't mention using distilled water of known KH or anything - just 5 drops of the reagent into 'some' tank water. Oh. and why oh why do thye come with black suckers rather than clear ones? These are minor points and would not stop me buying any more.
Thank god for this post which inspired me to buy them in the first place. I give them a glance every morning and has taken all the guesswork out about Co2 levels - it's already saved a lot of tests and calcs - thanks Hoppy!