I have used both NO3 and PO4 test kits from Sera and found them to be easy to use and accurate enough for home use.
The nitrate test requires a 20ml water sample to which is added drops of a liquid reagent then a powder reagent and finally another liquid reagent. A result can be determined after 3 - 4 minutes, but you can see how strong it is going to be within about 30 seconds. A tip for this test, I have found the best way to compare the result against the colour chart is to hold the vial slightly above the paper rather than sit it on it, this seems to give a truer indication of the colour saturation. If you set the fial flat on the chart then the liquid appears to be darker than it actually is.
The Phosphate kit has a similar procedure, however the directions specify that you read the result exactly 5 minuites after adding the final reagent. In this test it is a little harder to differentiate between the shades of blue, particularly between the 0.5mg/l and 1mg/l ranges, but if you use natural light rather than fluros it is a lot easier.