This is as I suggested in my earlier post; an improvement would be to use a sheet of paper between the indexer and the vice jaws to increase holding power; I do not think the holes he drilled are particularly handy, as the indexer is more used in the position where the spindle is parallel with the table slots; of more value would be the milling of slots along the indexer's axis and at 90 degrees to the axis, located in the center of the lower surface; these would be the same width as the table slots and about 1/8" deep and keys would be made to fit them about 5/8 thick; they would have drilled countersunk holes centered on them for Allen head screws to fit into tapped holes in the fixture at each side. The fixture can then be located accurately on relation to the machine's axes and clamped in place on the table. If odd angles were needed for particular parts being machined, of course the keys can be removed. Personally, I do not own a spin indexer at this time; I had one and never really found a good use for it, I use a dividing head for such work.
Most of what I saw on the videos seems unnecessary for practical purposes. Before I viewed the videos, I supposed that he was going to mill key slots, hence my earlier post that was not completely germane to the situation as later revealed in the video.