I don't always think about how/why filters works, as it's secondary to it simply working. I'm a user of filters, rarely a programmer (and even then, generally in reverse engineering).
It seems to be aware of colors, sensing overlap of black/white edge pixels (color bleeding), as well as errant noise (temporal averaging).
I don't see what you mean about flicker or yellow.
Start at default 50%. That's generally best. Less rarely ideal. More can blur and actually lose true color, so be careful. Yes, eyeball it.
"Show noise" should always be looked at.
You'll find most
VirtualDub and Avisynth filters have pathetic documentation, if any at all. Avisynth is actually worse than
VirtualDub. This is something I've griped about for 15 years now, sometimes pissing off fanboys and even the filter devs. It's often shrugged off as "the dev made the filter for himself, be lucky he shared it", which is just a cop-out excuse. Some filters are entirely indecipherable, and thus rarely mentioned, never used. So in terms of "what does this filter do, exactly?", it's like the Tootsie Pop commercial: the world will never know!