Obvs it's not permanent. Mostly just unique and delicious... and not that harmful either coz zero chemicals! In an interview with the Metro, the salon advises that the subtle colour will keep for around few weeks depending on the hair: ‘Colour aside, Nutella is good for the hair as it makes it more shiny.’
However as you've probably already guessed, most comments on the video are just crying about the waste of delicious chocolate spread!