It would be ok. You divide the ppm by 17.8 to get the deg KH. Technically I think it depends on what Carbonates you have in the water but ive used the Palintest on my aquariums for years. If you have access to RO water you can check the calibration of the tests, there is a thread about doing this :
Add 879.2 milligrams of baking soda to 10 L of RO/DI water for 2.93 dKH.
Add 1.6 grams of baking soda to 10 L of RO/DI water for 5.26 dKH. Fully dilute.