I'm gonna go against the group here a little. I agree that API's alk test doesn't have the necessary resolution to be useful. It's as accurate as it CAN be, but the lack of resolution sucks. That's especially troubling with alkalinity which is one of the most important portions of chemistry to maintain happy calcerous organisms. So yes, a hannah meter or salifert kits would be reccomended for alk.
For calcium though, I use the API all the time. Sure, it's resolution is only 10ppm, but what do you really need more for? I've tested it against salifert a bunch of times, and both are always within 10ppm of each other. Furthermore, IME, maintaining calcium is the least important piece of reef chemistry. Corals don't care if your calcium is 390 as opposed to 400. They'll care if it's 340 instead of 390, sure, but 10ppm differences which is the resolution of the API kit are meh.