Slasher Feat vs. Swarms

Not sure if this is the place to ask.. but I am curious if the abilities granted from the slasher feat from Tasha’s Cauldron would work on swarms. More specifically:

Once per turn when you hit a creature with an attack that deals slashing damage, you can reduce the speed of the target by 10 feet until the start of your next turn.

When you score a critical hit that deals slashing damage to a creature, you grievously wound it. Until the start of your next turn, the target has disadvantage on all attack rolls.

The argument is, using the slasher feat to lower an opponent’s speed would likely consist of something along the lines of slashing at the legs or heel, or something along those lines to debilitate your foes. Or on that crit you could be slashing a big gap out of an attacking creature’s arm or hand… if the creatures in a swarm are constantly dying as the swarm’s HP drops (assuming this is how it works based on the damage drop when swarms hit half hitpoints), then would these abilities technically work on a swarm or not?