I have been using API test kits for many years and they have been good enough for following a cycle in fish only or soft coral semi-dirty reef. Or detecting the odd pretty nasty ammonia spike (in bare qt's I used to run). I won't post anything that I haven't directly experienced myself.
I have noticed nitrate test kits to give different readings from one kit to the next but then I'd been using the first kit for months and the degree of difference was minor in terms of what I was trying to measure.
My opinion and this only my opinion is they are a good enough indicator of what's going on nitrogen cycle wise but I have no real experience in using these kits down at a very low level of nitrate <10 ppm ish. My sort of area with with FOWLR is 10 ppm - 40 ppm or OMG!
I was keeping damsels then and I'm not now so I'm getting a Salifert again to test for nitrate. I will use both at the same time out of curiosity. I have used Salifert nitrate tests before but found the top down reading more difficult.
Maybe I should just buy a UV/Vis spectrophotometer on e-bay!
just thought I give an update, I dosed 2ppm ammonia a few hours ago today and according to my results it’s already being converted to nitrite, so all is still going well cycle wise
also got my new lights, tanks looks much better IMO