They should of course have a minor effect in combat and not be overwhelming to be called overpowered or get nerfed.
Here are some perks as examples:
- Rapid Recovery: "You regenerate health 0.75 seconds faster. Reaching 40% HP or below will cancel this perk for 15 seconds."
- Guardian SV2: "When you reach 20% HP or lower, a shield will be instantly deployed at your location. This shield will only block 1 bullet and breaks afterwards or in 3 seconds. 2 minute cooldown."
- Acrobatic combat: "You move 5% faster and the distance needed to take fall damage is a bit longer, however you're slightly weaker to knockback."
These examples aren't too strong and in certain combat conditions they would be useless such as the Guardian SV2's shield being useful if you're running away or against weapons with a cooldown such the sniper or rocket but useless against pistols, rifles, and shotguns as it only blocks 1 bullet.