You have to ask yourself, what you want to test?
I have a calcium reactor and use an alkatronic to assure my alk is stable. I don't use the provided pump that is supposed to dose alkalinity. But alkatronic comes with a wireless power switch that you connect to your CaRx solenoid and have it turn off if parameters get too high.
As for the trident, I asked myself, "do I really care to have a daily reading of calcium and magnesium?" And the answer was No. Especially if you're using a CaRx it is extremely difficult for calcium and magnesium to change without seeing it with alkalinity first. For me, automation for an SPS tank can be boiled down to alkalinity, phosphate and nitrate. All those other readings are for the tourists!
The main reason for choosing alkatronic over KH director or trident was reagent costs... reagent for the alkatronic and KH director can be DIY'd for far less than the monthly cost of the trident. And the only difference between KH director and alkatronic is that alkatronic dilutes the same reagent that the KH director uses 4:1. Meaning the overall cost to make reagent is 4 times cheaper than the KH director.
And lastly, I have an apex too, and one of the chief concerns is not having the ability to have apex use the information from alkatronic to do certain things (if I wanted). All you need is a PM1 module and alkatronic can communicate with apex.
So for me, the alkatronic is hands down the best choice. And the company has just announced mastertronic that will be able to test phosphate and nitrate.