I have an API master set, a JBL ph test set and a nutrafin master set unopened so cannot comment on the latter.
I prefer the JBL kit over the API as the JBL helps to match colours by taking account of the colour of the aquarium water i.e. you have two viles 1 with tank water + regent and the other with just tank water. The tank water vile is placed over the coloured portions of the chart and the regent over the white portion until colour match. Easier than the API which sometimes requires a bit of guess work and can change with different light source and I suspect more accurate especially if you have tannin or other colorant in the water! Gives a different reading than the API about 1/3 ph..