As a pally healer, I confess they're definitely something you need to have already maxed your gear ilvl by every other possible means before attempting. Especially in random groups where you're going in with people who may be sub par performers. They can wind up being very long boss fights with players taking a lot of damage unless they're on top of their game. Even with careful mana management, there's still plenty of times I've ended up on 2% mana in LFD groups. Finding it much easier with my Druid, but I do prefer the pally and find that while there's still plenty of ungeared players it's particularly brutal on that class of healer.