question about perks *Zombie hunter*, *J'avo killer* and *Critical hit*

[Andrew™]

About Zombie hunter and J'avo killer
It says they increase strength of attacks. But I don't understand, does that mean they increase Melee damage against them, or it gives more damage to your weapons against them?

About Critical hits
Do I understand that correctly? it means that it gives more chances to make a lethal headshot?

[Akatosh]

that mean they increase Melee damage against them, or it gives more damage to your weapons against them?

Both, melee and weapons.

About Critical hits
Do I understand that correctly? it means that it gives more chances to make a lethal headshot?

Yes