Excellent kit which comes with clear instructions and is very easy to use.
The first test i carried out was on a recently acquired Audi which I suspected had a head/headgasket issue and the test came back positive (the liquid turned from blue to green within a minute or two). The diagnosis was later confirmed by a trusted garage who carried out their own test and found exhaust gasses in the coolant.
The second test i carried out was on a SEAT which has been suffering from coolant loss for at least a year or so. As I'd already bought the test kit for the Audi i thought I would give it a go with this car too. Again the test came back positive (liquid turned blue to yellow very quickly). This diagnosis was also later confirmed by a garage who found the EGR cooler had failed.
I also tested our other vehicles and thankfully in those cases the tests all came back negative.
In summary a really useful kit, very easy to use and in my experience 100% accurate.