I've not used Triton but have heard good things.
I have used ATI's solution and so far it has been pretty reliable. It showed that I had a low salinity. I wasn't sure since my kits showed here that it was fine. Posted a few questions here, few people asked if I have a reference solution, I didn't, then picked one up, recalibrated, and sure enough new results matched ATI's. So it seems to work. My Tridents results are similar to ATI's and within error of margin. I've also run manual tests using water at the same time I collected my tanks sample to send in and it is also within reason. Nothing has been off. One more the RODi water test with ATI is free and interesting enough it would report that I should change it. After a while I finally did and those reports are no longer there.
How accurate it is due to algae or other things going on in that tank I do not know. It has always been of my opinion if you have say green hair algae or another outbreak and manual tests come back with low nutrients, well, it could be because the algae is consuming it. If that makes sense. I'm not sure if this is or will be your case but algae does consume stuff...
In any case ATI, Triton, others give a nice overall view of your tanks water quality within each of the testers processing methodologies. There has been some discussion on quality but the two you listed while a bit more expensive have been reported, by hobbyists, to be more consistent. Doesn't hurt to have one done. I get about 2 a year done just because.
