Cutting with a sword is trickier than you'd think. Just making a clean cut in the first place is hard. If you do it wrong, then typically your cut is messy or you just bang things around. Unfortunately I'm not very good at it and usually things go flying even with a "good" cut.
But this guy is amazing. Some of his cuts are so clean that the top and bottom of his targets stay together after he has cut them in half. Wow.
UPDATE: More Tameshigiri (mat cutting) from James Williams. His first and second vids imply he is using Bugei swords.