Having run the halo device at Silverstone on Tuesday, Pierre Gasly has revealed he is not in favour of it as F1 should "always" be open cockpit.
The FIA is planning to introduce cockpit protection next season with Ferrari's halo design leading the charge.
However, up until Tuesday morning only Ferrari have ever tested it.
That changed when Gasly took to the Silverstone circuit with the device fitted to his Red Bull racer.
And although he said it didn't change much, the French test driver would rather Formula 1 avoided cockpit protection.
"It doesn't change much," he said. "It looks a bit weird from the inside, you can see that you have something on top of your helmet.
"Also the vision when you look straight you kind of see this triangle on top.
"I don't really like it. For me, F1 is always open cockpit and it doesn't look really like that with the halo.
"From the inside it doesn't change much so we'll see what they say about it but I think F1 should stay as it is."
Gasly was slowest of all at the end of the day as the 20-year-old covered just seven laps during the morning in the dry because of a wiring problem.
He returned to the track in the afternoon, adding a further 44 laps to his tally in the wet.
He said: "This morning we didn't run much but in the afternoon on the inters and the wets we did some good work. It's always good to get some running in the wet and hopefully it will give them some good information on the car."
Enjoy the full experience of the 2016 FIA Formula One season on FOX Sports Play, where you can catch LIVE races from angles unseen before, exclusive interviews, behind the scenes, in-depth analysis and so much more. Don’t miss it!