Nico Rosberg, Carlos Sainz, Nico Hulkenberg and Daniel Ricciardo have offered positive feedback about the latest evolution of the 'Halo' cockpit protection device followed its most comprehensive real-world test yet at Spa-Francorchamps.

Following the FIA's plea to teams urging them to help further the device's development for a 2018 introduction, four teams - Red Bull, Mercedes, Force India and Toro Rosso - would run the controversial device for varying programmes during Belgian Grand Prix FP1.

Significantly, Rosberg completed two runs, with the second on the super-soft tyres seeing him stop the clock at 1min 48.348s, which would go on to stay top until the chequered flag. As one of the device's most vocal advocates, the Mercedes driver was impressed with the safety gains.

RESULTS: Belgian Grand Prix - Free practice results (2)

"It was good to try it and they've done a great job with it because it doesn't disturb me at all when I'm driving and increases the safety a lot," he said. "I know it's not nice looking from the outside, of course, it doesn't make the cars prettier but if it's such a big step in safety then I think it's a good thing."

Ricciardo and Sainz, meanwhile, were pleased to note that visibility - their main concern - was not as impaired as they had expected.

"Visibility is not a problem," said Sainz. "Obviously when you leave the box, you have this thing in the middle which disturbs you a bit, but at the end of the lap you don't even notice it's there anymore. Your eyes get used to it, they get used to looking across it, that's why we have two eyes! That's it really.

"It is definitely still a work in progress," added Ricciardo. "The first time I've run it - I'd only run the aero screen before. So it was definitely different. But it was definitely good to test it, and to test it here. That is what we have to keep doing for now, so more drivers can test it before the end of the season. And just getting feedback. So I will give some feedback tonight. We've been given a sheet, a bit of homework. Generally speaking, not too bad."

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Having criticised the prospect of such a device as recently as the German Grand Prix, Hulkenberg admits he was surprised by the relative lack of disturbance.

"It was a weird feeling. I don't know, it felt weird. To have something there which limits you going forward was obviously a new experience. I have to say the visibility wasn't too bad. I don't think that was a big issue but certainly it will take time to get used to."

Dubbed as a chance for the Halo to get a good visibility test by coming through Eau Rouge at racing speed, Rosberg says there is scope for making the design even tighter.

"[Eau Rouge was] No problem at all, you don't even notice the top part. I think they can even come down with that because LMP1 is lower anyways. So for sure they could go lower."

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