Drilling a square hole is nothing new. I've done it 50 years ago, same principle, only thing different, we used a hardened guide plate clamped to the top of the work piece. The cutter was 3 flute like in the video, which was mounted in a floating holder. The cutter followed the profile in the bushing. the flutes were not sharp. only the end did the cutting. Still have some bits in my toolbox.