Seachum Ammonia Alert???

My fish store was out of ammonia testing kits that I usually use and I was out at home. I bought a Seachum Ammonia alert thing that sticks inside the tank and the middle disc changes colors. I am getting a 0 reading on ammonia, which is what I expected, but how accurate are these? They seem so much simpler and cheaper than traditional testing. The instructions say that they will work for a year. I don't test ammonia often at all, basically a day or two after adding fish or if I notice any changes in nitrite or nitrate and once a month just to be sure. So am I ok relying on this, I have never used anything like this before or seen one. Thank you