<grin> This got a lot more interesting (if less of an amusing tease) when I realized that closed caption English was on offer.
Korean sounds more like Japanese than I would have expected.
It was a cute video, but I think that the tool you were asking about was in part 1 at 14:50. It looks like something I'd do with a string hook, but not as fiercely. I'll go back and check.
Surprising. String leveling and hammer mating are critical IMO. I suppose if the hammer is mushy enough it might matter less but I'm not even convinced of that. I use Ronsen bacon felt and am fastidious about string leveling and hammer mating. I think you should be too. "String leveling" is a bit of a misnomer because the important thing is that they are on the same plane, not necessarily level to some point of reference. But it's not less important.
I understand that there's a trend to reject all traditional protocols. I think it's reached toxic proportions, honestly. Some protocols have less of a foundation than others and are more habits than necessities. But many have a real basis and while it's good to question the basis, throwing everything out for its own sake is a mistake.