fighter weapon focus

(this about 5e again)

so i wanted a thing thats more than the fighting style at level one to make the fighters seem more different than each other. ive seen a couple different approach to this - i think more likely most people would swap out the fighting style, or the battlemaster steez for this kinda stuff- but i like it stacks with fighting style, and i think swapping out the fighter's self heal for some weapon steez gives me enough space to work with, more than you get with jsut fighting style, and im playing with the essentials kit, which i like because its sort of a new basic - and essentials kit never mentions the battlemaster, so this might work in an alternate universe game where theres no battlemaster, and this 'weapon focus' ability can also round out the fighter style sidekicks in that book. ahem, 5e voice...

Weapon Focus

At first level, you can either choose a Weapon Focus or gain the Second Wind feature.  When you level up, you can choose to replace your Weapon Focus with a different Weapon Focus, or choose to swap a Weapon Focus for Second Wind, or Second Wind for a Weapon Focus.

If a Weapon focus ability calls for a saving throw, the DC for that roll is your Maneuver Save DC.

Maneuver Save Difficulty Class: 8 + your Proficiency Bonus + your Strength or Dexterity modifier (your choice).

Choose one of the following abilities for your Weapon Focus:

Trapper. When you hit a creature that is medium or smaller with an attack using a flail or whip, as a bonus action you can cause the target to either succeed on a Strength saving throw or be knocked prone. When attacking a target with a net, you do not take disadvantage on the attack from attacking at long range, or from making a ranged attack in close combat.

Secret Crossbow Arts. You ignore the loading property on crossbows. You can use a bonus action to attack with a hand crossbow you are holding.

Blood Drinker. Your attacks with daggers and darts do 1d4 additional damage. When you reduce an enemy to 0 hp with a dagger or dart attack, or with any weapon that deals slashing damage, you can immediately gain temporary hit points equal to your Constitution modifier + 1 for each level you have in this class.

Punch Through. When you hit with a reach weapon that deals piercing damage, or with a weapon that is thrown like a javelin (including a spear, trident, or dart), you can hit a second target with the attack so long as the targets are within 5 feet of one another, and you can draw a straight line from the attacker through both targets.

Rattle Bones. When you hit a creature with an attack using a bludgeoning weapon, that creature is rattled until the end of its next turn. (A rattled creature has a -2 penalty to its attack rolls.)