We'll probably never know for certain what would have happened to Charles Leclerc had Sunday's Turn 1 accident played out in Formula One cars without the Halo device.
The truth is, we don't really need to. The fact a car can fly over another at that part of the cockpit so violently, so unpredictably, at such speed, is argument enough in favour of it being on F1 cars. The images which have circulated online in the days since Fernando Alonso's McLaren vaulted over the Sauber at Turn 1 in Belgium show just how big a role the device played in deflecting his car away and, most vitally, taking the brunt of the impact of his front tyre as it slammed into the titanium structure resting above Leclerc's head.