Ugh. I hate it when people say that you can use something to cut diamonds like that's impressive. I get it, diamond is the hardest thing, so that makes it difficult to "cut", but that's a very highly technical definition of cut that doesn't really have much to do with how normal people use the word.
I mean, glass is harder than steel, but if you throw a steel ball at a window it's not the ball that will shatter. Tensile strength matters way more than hardness for most practical purposes, and diamond doesn't have a particularly high tensile strength.
The video talks about a neat tool. I just don't like the weirdness around diamonds. The flammable, easily shattered rocks are not in fact the most durable material in the universe just because they're hard. That's not what hard actually means.