I use the Red Sea Pro nitrate test kit and like it.
It's very easy to use. You have two vials, fill one with tank water and put it on the outside hole of the spinning wheel. Fill the other one with tank water and add the reagents according to the instructions. Once done, put it in the inside hole. You spin the wheel so that the first vial goes through many color pallets until it matches as close as possible to the second vial.