Ironically, that video shows exactly why the police shot first before getting closer.
If the guy on the vid had lost control of the knife hand for one second, his grin would have transformed into a expressionless bloody mask, and those stupid kids around would have started panicking a bit.
What people dont get is, if the last examples (bouncers, civilians, etc...) had guns at the ready and licence to use them, they would not get close and personal just for show. Except those that really want a show ofc, but those guys are either confident, or stupid, or both, and can still end up dead.