I disagree with you on several points.
Point 1) The tester is plenty viable for our hobby. With initial detection of 0.04 through a standard RODI system, even with a 0.03 accuracy range, there is *still* a detection that is statistically significant (at least 0.01 mg/l).
Point 2) Given my testing thus far, it would be very difficult to get 0.03 mg/l of chloramine into your system unless you mixed up straight undechlorinated water. Your water change is a percentage of total system volume, and in real world situations quickly reacts with any number of things in your tank and leaves corals relatively unharmed. In other words, we are not creating and maintaining concentrations at 0.03 mg/l in our tanks.
Point 3) I would rather spend money on consumables replacing carbon than DI for the simple reason that carbon is much more effective at removing a wide range of things than DI resin is. DI resin just polishes and removes the last remaining TDS, while carbon does much of the heavy lifting.