I’ll give a vote for the Hanna nitrate checker. If anything, it seems consistent to me over 100’s of tests.
But, at the end of the day, most hobby grade nitrate tests show a distinct colour change (faint pink to dark red) so you can also make a good guesstimate, 5, 10, which IMM is sufficient.
But I do use the Hanna colour meter because it’s likely more consistent than my eyes when comparing results.
In contrast, the Hanna phosphorus checker in PPB I use exclusively as the colour change is so,so faint, I can’t tell what it is by my eyes.
Both good in my mind.
I could not get the same from Hanna MG and CA testers, seem to vary widely.
The salinity checker I just didn’t trust at all.
I stick with refractometer.
Never ever got a nitrate as 0 with the Hanna.
I get a zero once in blue moon on both N and P, but when I retest, back to expected. I assume maybe just my error on process.