I wonder if it's supposed to stop swarming because foraging bees and house bees are unable to leave as a group?
It reads a lot like creating an artificial swarm, but in such a way that reuniting is easy because it's always been the same colony. On the other hand, miss a sneaky queen cell in the bottom box and all bets are off. Then again, I'm unconvinced the foraging bees will definitely build emergency queen cells at all because they'll still be aware that there's a queen present.
The section at the end where it says "in many cases this will be sufficient to overcome the swarming instinct" does make it sound somewhat optimistic. I think I'd rather go with a method that is pretty much certain to work rather than one that "works in many cases".
James