So all of this is hobby grade equipment. Each product has a precision range and a resolution range. For instance the ALK hanna checker has a resolution of 0.1 dKH and precision of ±0.3 dKH ±5% of reading. That is even before factoring in human error on things like measuring the correct amount of water or having perfectly clean tubes without French fries finger prints on the outside, or measuring reagent. The claimed precision for Trident is +/- 0.05 dKh for Alkalinity and 15ppm for Calcium and Magnesium. Much of that can be attributed I believe to it being an automated process which help eliminate some of the variables.
At some point it comes down to is repeatability. If my corals are looking good 8 dkh on the hanna OR Trident then that really all that matters in the end. I would not compare and contrast the two because it is a apple's to watermelon comparison as they are two different methods (automated vs by hand) of testing with different precision and resolutions. If the Trident calibration standard says it is X,Y,Z then you would hoped they sprang for lab grade equipment to provide those numbers or are using a lab that has the gear.
For now, I use the Hanna as it is what I have currently that I can use. When I get the time and can setup my Apex and Trident properly then I will migrate over to it. What I will not do is flop back and forth second guessing the other. Once the trident takes over and if fully calibrated then I will watch those numbers and what the corals tell me. In the end what the coral say is all that really matters to me and the number is just relative, it can be 8, 9, or 23...if the corals are happy and it is 23...well I will make sure it is 23, just as long as the test is consistent.
