I also use liquid test.
However, I do have one of those in my 75 gallon. They are cool when cycling cause you can see the progress your tank is making with eating up ammonia.
Only flaw that I see with them if there was a slight flux in the ammonia, the color may not change enough for you to notice, however ammonia can still be at level that will hurt fish, so its not a substitute for water test.
But very good if there is a sudden drastic change, when you walk pass you will know.