From experience, SuperFormance slugs really don't do a lot of damage to armor.
The only usage I can think is to kill scavs (that usually won't have good armor) and to be used sequentially - that would be when you load different slugs on the shotgun that do different damage, so you could put armor damaging slugs first, and close the deal with the SuperFormance.
Armor penetration is used to calculate (along with armor class) the possibility of a bullet penetrating and dealing damage to the body part, armor damage is used to calculate the damage done to the armor when hit. SuperFormance don't have much of any of those. (Source: https://escapefromtarkov.fandom.com/wiki/Ballistics)
One thing to note is, hitscan in Tarkov is kind of a big deal, so if your enemy is using a vest that only covers its torso (leaving the stomach unprotected), a shot to the stomach could potentially kill the enemy even if he has good armor. This also applies to a shot to the face or legs.
The chest or torso area is the most protected area in general because its vital, if you black out that part (i.e. lose all health points in it), you'll die. Most times people also aim for center of mass (torso and stomach area) when firing, so to counter these protections you can try to aim for head or legs as I said earlier.
Instead of SuperFormance slugs, I would recommend using Flechette (31 pen power/ 26 armor damage) or AP-20 (37 pen power/ 65 armor damage) for effectiveness all around counting with enemies using good armor. Oh, and also use a semi-auto shotgun if using Flechette (you need to shoot more rounds in less time to win against good armor with it).
The Health System is something I recommend you to know pretty well to understand all this: https://escapefromtarkov.fandom.com/wiki/Health_system
I also recommend to use a website or app on your phone to check the comparisons of ammo on the fly while playing. (for app on Android I recommend one called "The Hideout")
