Personally, I hate liquid test kits, I can't stand the color determination....is it this shad of yellow or this one. For anything I test, I look to buy the digital meters - yes, they are pricey, but when you consider how much money you spend on all of the other fish equipment and fish, and when you consider how often you test water params, the digital meters are so much worth it to me. I love a number to use, not a color and guessing game. And counting drops is a pain in the you know what.
Milwaukee carries a nice line of meters and so does pin-point.
My Milwaukee smart meter that tests ph, etc, and TDS is my favorite, I use that machine ALL the time and if it broke tomorrow, I would be on the internet ordering a replacement.
I swear by digital meters and I wish they had a digitial meter for all water testing.