Woa, interesting.
In this video it's more obvious that it isn't always seamless: Especially in close-ups, and with unusual lightning (shadows in the face, mood lightning in the eyes, ...) it doesn't work too well. Also it becomes a lot more obvious it really only swappes out a special part of the face , which means the entire rest of the head (and body) either fits or it doesn't.
But it works super well under flat lightning and from a distance - when the entire body is in the picture, it's almost unnoticable when only the face is swapped out. IMO with the right body doubles, and a bit care for set lightning, this technology could really work well to give short but amazing cameos.
But I stick with my opinion it should be only used for single, short scenes. The longer the scenes go on, and the more diverse the shots and blocking becomes, the more uncanny and noticeable it gets.
If they only use it for a handfull of shots (like Leias cameo in Rogue One) it could be amazing. If they overuse it, the trick gets busted (like with Tarkin in Rogue One).
