Flask of Supreme Power

Hey Guys, so I'm curious what the consensus is as it's my first time being a GM and first time playing WoW since TBC.

As a guild for Molten Core we supply our two tanks with a flask of the titans each. We have 5 flasks of supreme power in the guild bank. What's the best course of action to hand these out? Is it standard to hand them out to certain classes? Do we make the guild members pay for them etc?

Just looking for helpful advice. Thanks!