Unstable Concoction's damage and stun values are based on the time spent brewing it, so they can vary a lot, considering that each server tick spent brewing increases the stun duration and damage value.

It would be helpful when Unstable Concoction displayed the stun and damage values above the primary target, similar to how Chaos Bolt does it.

It should only show it above the primary target, and not every single hit unit, since all are hit for the same value.