TDLR: Helmets are a statistical form of protection from instant deaths from headshots and the opinion that only the altyn and killa helmets are useful is bad advice.
Rant Start:
I see the opinion on this subreddit that unless you are running altyns/killa helm, you might as well not run a helmet at all because everyone's mother is packing m995 and m61.
This is bullshit argument but people feel this way because of specific experiences where a helmet seemed to not stop a headshot. This is bad advice to give to any players, especially new ones.
My point is that helmets and armor are a STATISTICAL form of protection and not immunity from headshots. They just decrease the likelihood you die from a shot to parts of your player model. In the case of a helmet, there are still parts a lot of helmets don't protect. Even in the case of the most common helmets like the ulach/achhc, these probably reduce the total visible head hitbox by around 50%. Assuming 30-50% of bullets fired at you can pen t4 helmets (an educated guess, but a fairly reasonable assumption in my mind), you avoid instantly dying to a headshot a significant amount of times (around 25-35% with the numbers I am guessing with). You absolutely will still die to headshots some percentage of your deaths, but helmets are a great way to reduce the number of instant deaths you experience.
If you are taking in >100k in gear, weapons, and ammo into a raid (aka ~tier3 loadouts and above), isn't it worth the extra 15-100k for a helmet that will let you life through a noticable amounts of what would have been instant deaths?
Dying to a single bullet is frustrating but also makes this game so much more tense than other survival games. Please don't tell new players that all-but-the-best helmets are garbage just because you've died while using them before.
Note: the numbers I use here are my best guess and I'm sure the number of people with pen ammo in labs is a lot higher than somewhere like customs or shoreline. The numbers are an approximation to go along with my argument.
End rant.
Source: https://www.reddit.com/r/EscapefromTarkov/comments/fuj7rv/bad_attitude_on_here_about_helmets/