Not sure why you think reefbot would be more expensive over time. The cost of reagents, for 3 test kits, would be negligible.
We're talking about a 300-400$ price difference between a box that does 8 tests and the other box that only does 3.
Accuracy (and build quality) are going to be the major factor for people deciding between the two options. If Trident doesn't have an obvious consistency/accuracy benefit over the reefbot, it going to be a hard sell for most.
I guess we'll have to wait and see, but 500-600 seems mighty extreme for 3 tests. 400 seems much more reasonable.
Edit: 40$ for trident reagent? Is that for all 3 tests?