Hardline basically lets you get a killstreak with one less kill, so if you have UAV selected you can get a UAV with a 2 killstreak. Personally I don’t like using this, it is fine for low kill streaks, but if you want to get high ones you will probably need stopping power or more ammo.

The Hardline Pro upgrade gives you the ability to get a deathstreak with one less death, which is handy cos you’ll probably die a lot more with this perk equipped