I agree that their mouth movement wasn’t particularly natural, but I disagree that it isn’t enough to fool most of us if we’re unaware. We’re not fixing our eyes on a person’s mouth while they talk.
Think of the scenario where someone edits a few seconds of a 30-minute interview. They make the interviewee go from saying they hate drugs to saying they love drugs. Even if you weren’t expecting that claim from that person, would you go back and recheck their mouth movement, to be certain if it was edited or not? Unlikely. Even if you would, I’d wager most wouldn’t, including most of us that could detect it.
For propaganda, this will be great. The thing is, you don't even need convincing videos for propaganda to work.
For truly scary things, like falsifying evidence, I think it will be awhile before this will get past expert analysis, or even a group of people on Reddit trying to prove it wrong.
In the long term, video will simply be treated like photos are now. With disbelief.
It can also be used to 'ratfuck', if a video is released with a politician saying a gaffe, they can release a bunch of similar but fake videos and then claim that 'all of them' are fake. The confusion would sow doubt- the technique could be used offensively as well as defensively.
Think of the scenario where someone edits a few seconds of a 30-minute interview. They make the interviewee go from saying they hate drugs to saying they love drugs. Even if you weren’t expecting that claim from that person, would you go back and recheck their mouth movement, to be certain if it was edited or not? Unlikely. Even if you would, I’d wager most wouldn’t, including most of us that could detect it.