Really wont be using flasks in Classic TBC though. They will launch with 2.4.3 and you will be using 2 elixirs, probably not flasks.
Healers will be using Elixir of Major Mageblood and Elixir of Healing Power for sure. The flasks is only 25mp5, while mageblood gives 16mp5 and healing power gives an additional 50 healing. +50 BH is worth way more than 9mp5.
Hunters use elixirs, locks use elixirs, mages uses elixirs. Flasks will only be used for more casual guilds progressing through content and dont want to pop elixirs every time they die.