I think the fundamental difference is if I lobotomize a Pest, it still devours quanta. If I have a shield, the pest still devours. As long as the Devourer is alive and kicking, it will devour. But with the leech, sheilds and CC will stop the loss in quanta. Also, fractaling a devour gets a certain amount of instant satisfaction whereas you can't immediately play the leeches until next turn.