I've used the alk, mg, ca and po4.... I like their kits simply because the end points are very clear. It goes from blue to yellow... or pink to blue....Its not wimpy shades either, its a very distinct color.
Alk is sensitive to .5 dkh, but per instructions only reads in 1dkh. You can increase the water tested by double and then divide the drops by two to get it to read to .5 dkh. Goes blue to yellow.
Ca is very good, goes pink to blue. Each drop is 25ppm. Sensitive enough for me.
Mg is good too... same as the CA but sensitive to 100ppm. One of the easiest mg kits around. Double the volume testing and drops then divide the indicator drops by half to get to 50ppm. Watch the expire date, the 12/08 ones were misprinted to read multiple by 100 when its actually 75.
PO4 is okay as well... would much rather use a hannameter, but I am not willing to plop that change.