im not going to speak bad about any test kit out there, but i will say, as i said previously, the one you had is doing something funky. it should have some sort of color, wether ammonia is present or not.
i will also not say that the kits are accurate, nor will i say that they are innacurate. lately, it seems that they are all over the place for me, and i will explain how.
i personally have two kits. a red sea kit, and an API kit. if i want a quick test, i use API, but if i really want to confirm something, i use my red sea kit. here is why. i have found, by process of using the LFS to test my water with their API kit, that my nitrite test doesnt reflect the same as theirs. i dont trust the API nitrite kit i have, because i know its wrong (per matching results from my red sea kit and the LFS kit). i also know that my API ammonia kit tests .5 higher than the LFS and my red sea kit as well.
on the other hand, before i needed a refill, my API results were pretty accurate, minus the .25 that my ammonia part always showed, but is not surprising.
i trust, to a point, what my API kit shows. right now, i only trust the nitrate test for it, because the other 2 are proven to be wrong, but in the instance of yours, i would be hard pressed to say i trust the ammonia reading simply because its giving you no color whatsoever, it seems.