I run both types of reactors in different systems, Kalk stirrers are nice for bigger systems, but honestly don't run one in my smaller system's. Your no more likely to overdose a system with Kalk than any other additive. The key to any dosing system, two part, or kalk, is the accuracy of your timer, or measurement. The systems that I run stirrers on, are basically on timers ( apex controlled with safety's ), and dose a full saturation of kalk at given times of the night. The kalk dose is not directly responsible for top off, there is a separate top off system that catches the system up during the day ( this is important for fully saturated kalk ).
On a smaller system, you can dilute the kalk to match your top off consumption, and use with an ato. Kalk is cheaper to use that 2 part in my opinion, but can be a pain to dial in, and often needs to be adjusted with ca or alk to balance the system.
As for Bio Pellets, there is no rocket science to it, but its not the holey grail either. You don't use bio pellets, and vodka at the same time, both being carbon sources, its redundant and hard to measure if you combine. I wouldn't recommend carbon dosing of any kind without investing in some research, you can do more harm than good.