@James @markojp I can see your apprehension to this idea and so it was for me until I saw it in action.
NO! Its not like yelling at your spouse. (BTW I’m old enough to know better than to do that as it cause personal suffering)
Video is important as it shows what HAD occurred.
This is an instant feed back for an individual that understands to some degree of what should be done as it helps them get there with immediate correction. My sons response was “great now I understand, it makes it easy”. What attracted my attention was that in mid-action a correction occurred, I could hear it being said and watch it happen. Instant.
Swimming like skiing (and most other sports) has the instructor separated from the student, only interacting well before or well after a correction is needed, making it difficult to get the minor correction across at the correct moment. Funny thing racing, industry and other fields use similar methods to walk there charges through activities.
This is just the next tool which makes all this easier.