fyliu,
I thought the video had pretty good details and hints. Its 60 minutes... so about 8 minutes for each subject.
In the splice (whip) graft section...after the scion is wrapped with parafilm, they also use parafilm to secure the splice graft. They specifically mention "stretch and pull this parafilm"...which to me means make it tight, but do not state that tightness is absolutely important...it is only implied. The grafter then secures the graft with additional row of wrapping (white nursery tie tape), since parafilm is not that strong at the graft union.
In the cleft graft 1 video, they wrap the scion and graft union the same way as the splice graft...However this grafter gives the graft union rigidity with electrical tape instead of nursery tie tape!
You are correct, the intricacies of scion preparation for mangos is not addressed (i.e. leaving the leaf-trimmed scion on the tree for a week before cutting the scion off the tree). Only citrus and avocado scions are addressed...much different technique in my opinion than mangos.