I have one, and really like it. That said, it reads 2 decimal places. I understand that even a reading of zero on this device still may be enough phosphate to be a problem.
It is super easy. I fill both vials with aquarium water to the clearly marked line. You add the packet to one. The "clean" vial is the control and goes in first. Then the second (the unit clearly tells you when its ready).
The problem comes that it takes 3 minutes after this to get a reading. The problem isn't with the 3 minutes, but rather that the reading doesn't stay on the screen for more than a few seconds. Therefore, you need to be looking at the screen at the conclusion of the three minutes. Sometimes I'm not.
It has made checking phosphate levels much easier for me, and well worth the cost investment.