I've done kalkvasser, 2-part, and used a Ca reactor (at different times). I really think that what works best for you depends on the size and demands of your system.
For a smaller system, dripping kalk is good, although I found the mixing and constant refilling a chore. If you dose via top-off water, unless you mix a very weak solution in your ATO reservoir, you'll end up with a lot of precipitate that could eventually clog things up; it's also a very hit-or-miss approach. I never did use a kalk reactor because I wasn't that into the whole kalk thing. I did use a medical peristaltic pump (eBay) and IV bags, which made it easier. Adding kalkvasser helps support the system alkalinity, but does not add any carbonates, so you may still need to do that. For me, kalkvasser was very low cost, but high maintenance.
A Ca reactor is great for a larger system. Once dialed in, it's very low maintenance and keeps everything very steady. Highest initial cost, but lowest maintenance cost, IME. Since it dissolves actual coral skeletons as its source of Ca, it also replenishes alkalinity and at least some trace elements at a near-natural balance. Set it and forget it, yes, pretty much.
2-part dosing is great for a medium-sized system. A good dosing pump makes things very hassle-free except for refilling your additive containers from time to time. The dosing pump really isn't necessary, but it sure makes life easy. You could spend almost as much on 2-part as you would on a Ca reactor though, especially over the long term. Mixing your own solutions (BRS, for example) can reduce the costs significantly. For me, this is also very much a set it and forget it method. I only test for Ca and alk every 2-3 weeks, and only occasionally need to make small corrections to stay on target.
Those have been my experiences, at least. I think the first step should be to figure out exactly how much Ca and alkalinity your system is consuming each day. Once you have those figures, you'll know just how much supplementation you'll need, and it will be easier to decide on the best approach.