I’ve started using Potion of Concentration on some of the more difficult fights more out of necessity than anything else. That additional ~10000 compared to the standard issue mana potions offer a sizeable advantage. The catch is that you need to find a time during the encounter where you can spare the time. Although you can interrupt it anytime, don’t do it. Maximize the gain. There were times where I’ve cheated and took a tick or two of needless damage to squeeze out as much drops as I can out of these potions.
Heroic Magmaw? Any of the head phases.
Heroic Maloriakk? I use it during the first part of any Dark phase.
Nef? Once I’m on a pillar.
Cho’gall? Any part where there is no abomination (Or whatever its called) up.
I’m not sure if I can find a spot for it consistently on other bosses. I’ve only recently started using it. It’s going to take a bit of trial and error until I find the perfect sweet spot on encounters like heroic Chimaeron, Atramedes, and Theraliona.
Also, ding guild level 25! It took us about 4 months but we did it!