Sorry, I keep forgetting your kalk reactor question.:lol: Sometimes you have to remind me a few times.

As you already know, Deltec has the best reactors, but dang are they expensive. I have heard nothing but good things about the GEO reactors, and the twist off cap for refilling sounds really nice. However, with a pump driven reactor you are going to need to clean it at approximately the same time as your refills anyways.
Dosing pumps like the Litermeter are by far the best way to administer kalkwasser. I'm not sure how all of the other ones work but with my LMIII, you just set how many liters per day you want to add and it doses 1/150th of that amount 150 times throughout the day. This keeps the doses nice and small and spreads them out throughout the whole day.
You can also do automatic water changes but you need to purchase a couple external modules. You can also use the external modules for other things. I stopped doing automatic water changes after a while and used on module to add fresh saltwater to make up for what the skimmer was taking out. I used the other module to add top-off RO/DI water. This allowed me to precisely set how much kalk to add to keep the levels stable and then use the other module to dose the remainder of daily evaporation with RO/DI.
If you want my personal opinion on automation, I say stay away from it. The more gadgets you have on your system, the more likely one of them is to fail. The aquacontroller is nice but I highly discourage anyone from using the X-10's as they are very unreliable, trust me, I know. The direct connects are the way to go. I haven't heard too much good about the Aquadyne, it just seems the Aquacontroller is a lot more popular for some reason. I don't know squat about the IKS and Aquatronica but have heard they are nice.
So what else can you do... hmmm.... pretty much anything. I have only used an Aquacontroller Pro so I'm not sure what the other units are capable of. With the AC pro you can control ph, orp, salinity, do, and temp. You can have it email your cell if one of those parameters goes out of a user determined setpoint. You can access it from across the world via internet and have complete remote control over the equipment connected to it. You can have it start turning equipment and lights off if there is a chiller failure and the temp starts to rise. And there is a lot more it can do but that should give you an idea to get started.