The reason for the recommendation of the HTH 6-way drop kit is that it is usually immediately and inexpensively available, and has a good pH, TA, CH and CYA test, as well as an OTO test that goes to 5 ppm instead if the usual 3. With steam-distilled water for dilution you can measure total chlorine levels fairly accurately up to 20-25 ppm. Using color descriptions you can measure/estimate higher levels. But you cannot get an FC or CC reading from it.

You can use any hammer to drive a nail. But if you plan on driving a lot of nails you'll want the best hammer you can find to hold up down the years. The K-2006 is the best "hammer".