Hey FarmerTy! Glad you asked this question. Please keep in mind that I have only had my unit in place for about a week. I chose to go with the Alkatronic unit. Here are my honest thoughts at this point about the unit.
PROS
1. Integration with Apex
2. Cloud-based so I can get alerts and have access from anywhere. Also operates as a standalone unit (no need for Apex, etc)
3. Vendor Presence. If you just look at how long there thread is, that tells you plenty.
4. Cost of long-term operation should be manageable (buy concentrated reagent and mix your own).
5. Design. Not oddly shaped which makes it more difficult to place when you do not have a ton of space.
6. Accuracy. I will explain why this was lower on my list.
7. Silent operation
CONS
1. Cost (you do get cloud access that others do not have though). Some other units cost less
2. Configuring device through cloud (not really necessary once setup, but would be nice to have)
3. Setup (was a little finicky getting setup (some user as well as device)
4. Bluetooth and Wifi cannot be used at the same time (Not a deal breaker, but would be nice to have them both work at the same time)
5. Support time zone difference (not an issue for me since I work from home so I am near my device when they are online. May be for others)
6. Need to have a low alk threshold. If you do not have tank water in the test vial, it reads 4.54 and will start dosing alk. This only happens if you do like I did and calibrate and forget to put the tube back in place, but still could be a nice feature to protect against stupid
.
NOTE: Below were initial assessment, but vendor resolve with flying colors.
My back and forth with the vendor is well documented in their thread, so a I won't go into too much detail about that. The current model does have noise which the vendor already has fixed in new production models and will be sending the fix to original owners. Glad that they are making that happen. What I will say is that alone has me sold on there product. They stepped up and responded appropriately.
Now to the device itself. It really is awesome thus far. Measurements are rock solid and if something changes more than 0.14 the unit test again to confirm. Prime example, I did a water change and it increases my ALK 0.4. The unit just so happened to be doing a test not too long after and read that it was more than 0.14 higher than the last sample so it tested twice. I haven't used every feature yet from the unit, but there are others that have in the thread and it works as expected. You can send the info to you Apex (any model) with good accuracy. From what I have read it is 0.01-0.02 off from the actual reading of the Alkatronic and what is shown in Apex. Now I personally couldn't have know that the unit would be this accurate until I had it in my hands. That's why I put it as #6 above.
I am in strictly monitoring mode right now and doing my dosing as needed. Usually not too much since I am running kalk. After a few more weeks of strictly monitoring and once I have it hooked up to my Apex, I will begin dosing. It absolutely helps knowing at any given time where is my ALK.
Update: 7/11/18: Don't know what I'd do without the unit at this point. I just add 63 SPS frags and 55 various zoa, duncan, etc to my 240 and the Alkatronic has made it look easy to accomplish. Getting great growth and I haven't even used my T5s yet, only running actinic all blue at 100%.
Another reason that I chose to go with the Alkatronic is because of the upcoming Dosetronic that will work in conjunction with the Alkatronic (or as a standalone for whatever you want to dose). I know that GHL has their ALK monitor and dosing pump, but I personally just didn't want to buy into the GHL system. From everything I read is that they GUI for their devices really need polishing (I know that the hardware is the most important, but if you cannot put the effort into making the user experience less frustrating, I'd rather be doing something else than stumbling around trying to figure something out). More details will be coming out about the Dosetronic and I was told should be available in Autumn 2018.
I have not had experiences with other monitors so I have nothing really to compare the Alkatronic against besides what you read online (I am sure you have already done a lot of research and that is why you ask this question in the first place).
Overall, I will say that it is a really solid unit that will continue to evolve and get better as we continue to provide feedback/enhancement request to them. They do seem to listen and the big part about them is that they are AGILE. I like that more than anything honestly. They have reacted to items that have been identified to them within a reasonable amount of time (not years).
Update 7/11/18: The unit is excellent and I am not just saying that because I spent the money on it (you know how some people try to justify there expense 
). If you are on the fence about buying one, get off now. I haven't worried about calcium or magnesium either. I just does with kalk to the alk I want and that's it. Will only check magnesium once a week if that. Looking into a CaRX because the Alkatronic is just that good.
My default interval is every 4 hours, but if you notice that the interval adjust when the measurement fails outside of the threshold you have setup in the config.
