The main idea of using the flaps is workable but may be a bit challenging for some to keep the cuts parallel. He's working with ideal rootstock and healthy looking, good caliper scionwood, so he may be getting good results despite a somewhat perfunctory technique. I'm often working with less than ideal materials, so I always wrap my scions with parafilm or equivalent and always shield to increase my chances for a successful graft.

I've found that when regrafting virginiana rootstock when the previous graft, say of kaki, had been lost to a hard winter that often the rootstock cambium is in less than ideal condition. I believe this causes my percent of successful grafts to decrease and the vigor of the grafts that do to be low. In this scenario I would recommend instead of grafting immediately to such a rootstock, to allow the rootstock to sprout and once the green wood is of sufficient size later in the season, to use it as the grafting site. This strategy allows you to tap into the tree much lower than would otherwise be possible and so avoid the damaged portions of the rootstock. It also allows you to harness the considerable energy of these sprouts to allow for a vigorously growing graft, which although started later will soon outpace a graft made directly to the rootstock trunk.