Info dump no one asked for:
These are actually Alderaanian consular security, as they are the security force assigned to and responsible for escorting senators and other dignitaries. Many rebel troopers, primarily on Yavin 4, utilized the same uniform or variants thereof due to the the relaxed nature of the rebel uniform standard.
My best guess for why this helmet is seen a lot with the rebels is due to the (surviving) Alderaanian security force joining the rebels and bringing their equipment, however it's not really explained.
Regarding the actual functionality of the helmet, I have no clue and I'm sure it was just because it looked cool a futuristic, thanks George Lucas.
This is known as the Paradox of tolerance