Step Turn:
The fact that it might have worked out nicely is not justification for doing it.
The justification for doing it was that having got down to the desired glidepath he wanted to retract a notch of flap rather than carry the extra drag he no longer needed.
There are a lot of things which can be done in planes, and will work out nicely if done under certain conditions, which still should not be done.
Yeah but I, amongst others, do not agree with you that reducing flap from 30 to 20 at 450' in a cessna is one of them per se.
Though I agree that change in those conditions should not create an unsafe situation, it is taking the plane towards an unsafe condition
The condition he was taking the plane towards was 450', flaps 20, on the desired glidepath.
It is poor form to get used to doing things on final approach which destabilize the approach, or tend to undo a landing configuration.
It is entirely feasible that the pilot in question possesses the modest amount of grey matter required to understand that what worked at 450' in a C172 might not be so clever at 100', or perhaps approaching the middle marker in a 777.