I just put one in my tank, nothing yet. BUT in my infinite wisdom I opened the package before reading the part that says don't touch the sensor and I touched the sensor. I'll update tomorrow as to if its working or not. Maybe I'll even take a picture.
See, my thinking was, if I can tell when it gets above ROUGHLY 30ppm, or 40ppm, then I'll do a change. I see no need to have to use a master kit if j don't have too. There's a serious convenience thing here.