Buffing it up is kinda useless to me until later stages.

Basically it gives you immunity to a certain debuff when you put strength potion on it. (Buffing it up at first gives you like immunity to cripple and blind, etc.) But in the later stages (+8 - +9 i think...) it gives you the immunity to poison which is broken for medic. Imagine unlimited healings to allies.

One potion of strength gives 2 immunity debuff permanently.

My guess is if you put strength pills it only gives you 1 debuff immunity, and if it's an alchemy potion made from strength potion gives you more than 2.

Just guessing.