As per the start of the video - it is an adaptation of an established UK pattern called Bob’s Bits. Paul Slaney, a friend from Wales, originated the Megabyte. He has been fishing it for years, to great effect, on the lakes and reservoirs he fished in Wales, and England.
It imitates large chironomids (“buzzers”) hatching on these stillwaters. The strands of seal, treated with some floatant, keep it in the film very well. It is fished mostly static, with the line affected by the wind and ripple, slowly drifting the fly along with it. Of course when cruising fish are observed, one casts ahead of the anticipated path and wants for the fish to pick it up.
Here is a fish I picked up using the pattern when I visited Paul in Wales one summer: