Wait, so did McLaren just opt to not go with a high nose? Gawd I hope it's quick to prove the other cars were wrong in their decision.
Nope.
Their car has been running a lower nose/chassis for the last few years, using the lower nose to run a lower CG and better suspension geometry. Their car last year almost met the nose regulations already IIRC, so this year's is only a slight evolution of that. Guesses are that the snow-plow they (and only they) run under the nose helps with airflow under there.
Conversely, most other teams have been chasing Red Bull's high nose concept to get more air under the car to play with further back, which requires the bump. It may not be an advantage right away, but it allows more flexibility further down the line, as per BBC's new expert guy.