Ahh, yes. Well it’s true. MES free acid it is an acid. More specifically a weak acid. And, sure you could use it as a PH down. Add it to water, and it will partially disassociate driving the PH. But, this is where we start to loose sight of the point of a buffer. A buffer only works within certain ranges tied to the pKa(s). And, to get near the pKa (buffering regions) you add or produce the conjugate base. Initially, with MES acid in pure water, there is no conjugate and it is not a buffer yet. Within the buffering region is where the magic happens. Once you are in that region, other mechanisms will cause PH to move, the buffer will resist those changes.
They, the calculator, creates the conjugate by using NaOH. We use KOH for hydro to avoid adding sodium. Both are strong bases and both create the conjugate. p.s. a weak base would work as well but the outcome is something not necessarily easily predicted. You might notice that many of the buffer calculators limit the range of the PH for a particular chemistry. This is because for a PH outside of that range (based on the pKa(s)), it is no longer considered a buffer (the chemistry is either deprotenated / protenated). The further away from the pKa, the weaker the buffer action becomes.
It’s not easy to decouple how one thinks of the buffer from the routine PH up/down adjustment / drift / etc. The intuitive feel simply is not there.
In the end, it boils down to everything being inter-related one way or another. We are just moving H+ and OH- ions around. But, not differentiating the actors makes it easy to miss the trees through the forest 
Yes, that is what should occur.
Yes, precisely the same thing is going on the chemistry in the cal buffers. The PH is adjusted to the calibration value using a weak acid / conjugate such that it is within the buffering region. The PH overtime can change due to CO2 entering solution, contamination, etc but the buffer will resist a change in the PH. Due to those reasons, the PH will change and is the reason they have expiration dates and is also why they tell you to dispose of any used calibration solution. It isn’t changing because of the buffer components.
I did read somewhere that you are supposed to PH adjust those beads prior to application. Soaking them in a PH adjusted solution perhaps. As to capacity, that’s an interesting question. I’d venture to guess that it would look similar to how a chemical buffer would act with the PH slowly changing as they absorb H+/OH-. Wouldn’t mind getting my hands on some to test.
I tore the storage room apart and no cord. Then my wife asked me if I had by chance put it outside with the generator. I scoffed at her and said I would have seen it, plus I was sure I had put it away after the last time. She just gave me that look, so I went outside again, and there was the dam cord right next to the generator in a storage box with the funnel, extra gas, etc. My excuse is the box had some snow on the lid… Yeah, she didnt go for that either 
