The Hanna checkers seem to be a mid point between the basic test kits and full automated testing. I have several Hanna checkers, including alk, phosphate, calcium, and pH, and look forward to getting the Nitrate checker soon. I sometimes struggle with color variations so I appreciate having a number.
I have the Alk checker and find it very convenient to use. That is the only must-have Hanna checker in my opinion. Their calcium and phosphate checkers use powder reagents. I do not like working with powder reagents.
I use the Alk and LR Phosphate regularly. I also have the calcium checker but rarely use it. I also have the Hanna Checktemp Digital thermometer that I use constantly. I was interested in the nitrate checker until I saw it takes 8 minutes and requires a lot of steps.
I was terrified to dose Coppersafe until I had the Hanna checker since so many people said the dosing mix wasn't consistent. I'm just paranoid, but its definitely nice to have. I'd like the PO4 one next.