When I worked in a lab about 10 years ago I used to use the Merck kits and found them very good. I liked the idea that the test sample was placed on the colour card and you looked down onto the card. Seems a much better method than holding up the tube next to the colour card as you can get different results depending on how the light is shining on the tube.
They used dry powders which you added using a tiny spoon. Dead easy to use.
I would still use them now but they're not that easy to get hold of.