I've got all three - Mastertronic, Alkatronic, and Dosetronic.
I've only had them a few weeks, and am still fiddling. I'll probably post more detail in my tank journal when I get them all dialed in, but here are some thoughts so far:
+ It's SO NICE not having to test anything at all. N and P in particular, I had mine testing both daily and it was very helpful in balancing my nutrient export
+ The machine is pretty reliable so far once it's set up. It maintains its internet connection, does what you expect it to do, etc
+ Customer support is excellent - both from CoralVue as well as when they've had to escalate directly to Focustronic, but that brings me to the first negative...
- The manual sucks. I a consider myself a reasonably smart fellow and a tinkerer, and I still had to hit up CS a couple of times for some strangeness during set up. I didn't get everything calibrated correctly, despite my best efforts, and was getting wonky test results.
- The app is just...OK. They are continually updating it, but it's really slow to reflect your inputs. You will make changes to the testing schedule, for example, and they don't show up for a while. Sometimes not at all, and you have to enter them again. It's just kinda clunky and unintuitive. This seems par for the course with all reef companies though, so I've grown to expect it. Reefbeat, Mobius, the AI one - they all suck IMO.
The jury is still out on how it integrates with the Dosetronic, but I've set it up to maintain N and P within a certain range based on the test results from MT, we'll see how it works over a few weeks. The Dosetronic part of the app sucks even worse than the MT. The scheduling is not intuitive AT ALL.
The Alkatronic, for anyone curious, is pretty awesome. It's the most straightforward to set up, has the best section of the app, and has kept my Alk super stable.