I think what you said probably works well. What he is doing, is controlling the bees environment, feeding, using the flow, etc. I'm sure he does well. But if you asked me which is better, and not just suggest what works, than I still do not like to use worker cells for queen rearing. If I use the same amount of effort, I would rather use queen cups, and forego the whole cutting of cells. I also know exactly how many cells too expect. I've used the method you suggest, and sometimes you get 12, and sometimes you get 24. My operation needs to be more efficient than that.
Many of the items listed previously, mentioned things like supercedure cells at a time of poor flow, at times the bees are not ready to make cells, under stress, etc. Very different than what your friend is doing.
I think the discussion should point out the methods your Friend uses, and the assumptions made, and even promoted in some bees books about supersedure cells found in a hive under less than ideal timing or circumstances. I have read, and some suggested, that when you find sepersedure cells, that these are the best that nature can give you. And that may not be the case. But that is entirely different than the controlled manner that this queen breeder is using.