I have one of these. Nice bits of kit, I use the Salifert ones though, as my nitrate test doesnt just do drops, it does rivers, and my phosphates test doesnt work. But personally I think itsb ecause mine is out of date.
Yeah, to be honest im not sure why they are cheaper, may be they do not give accurate readings? I have not really asked about the "accuracy" of this test TBH with you, might be worth checking it out before you purchase it mate.