I stopped when he split the brood nest in half by putting a box between. Adding a frame or two with a good strong colony.. OK, but I wouldn't split the entire thing in half that far with an entirely new box...
I had a grand idea at one point, and built SQUARE boxes... 19 7/8 by 19 7/8.. they held 13 frames each.. it worked, but as Robo said, they didnt use the outside frames. In this case, the FOUR outside frames. two to either side of the brood chamber.. Like Robo, I think its too much room..
Unlike most, I was taught that mediums allowed easier clustering and movement because it has two breaks instead of the one two deeps have... had a couple arguments about that, wont argue about it anymore.., it works, but so does two deeps.
I stick with the universal fit argument.. ONE size frame in supers and brood. I also like the weight of mediums. I still lift deeps, but could see problems in the future making that difficult..
Looks like those hives had 12 frames per box.. while I liked the depth of them
I didnt like the width, or splitting the brood chamber that way. He also didnt cut handles into his boxes..