I don't know why he didn't wear the Guardian helmet cap, and if he does return, I hope he does opt to go with it.
I assumed that a lot of players just don't want to look different than the rest of the team, but... other than one time in week 1 where an announcer pointed out specifically that a player had opted to use it in explaining the new rule... I don't think I've seen anything about players who've picked it, and certainly nothing unkind. A few times I've been watching games on red zone and noticed players wearing the Guardian cap in the close-up shots, but, once they go to the wide angle it's actually kind of hard to even pick it up that someone has it on. I can't believe any player is going to call another one on the opposing team a wimp, chicken, or whatever words I can't say on this forum, for wearing the cap. They all wear it for parts of preseason practice anyway.
Otherwise, I guess there's maybe a non-zero amount of limitation in the field of view to the sides... but it can't be enough of a difference, even for a QB, to bear the risk of yet another concussion.
Either way, I hope someone gets through to him that he should be valuing his long-term health much more than he's shown to so far.