[POE2] Is unique item with ''grant skills'' bug or feature?

I dont understand ''grants'' in poe is like got a skill and then you have to cost somthing like mana or mana reserve to use it. but in poe2 u just got the skill and can use it without to cost anything for my case is sand of silk shrouded can use blink without to reserve spirit and The Coming Calamity
Heroic Armour can use herald without any reserve. so i just want to know it is a feature of the game or just bug?