My take on the Echo-Revenge HotP deck.
Just control the board until you can play your combos, play smart with removal, and don't be afraid to suicide your lifesteal units if you have to.
Devouring a
Piercing Grief end of turn is almost never a bad idea, even though it sucks when you immediately draw it.
Even if the ideal scenario is to give a revenge unit or the hero Echo with
Elysian Pathfinder, even hitting something like the
Temple Scribes isn't awful.
Versus aggro, don't be afraid to slam a
Piercing Grief turn two just for some life or a
Blistersting Wasp for some board presence.
Another combo to keep in mind is holding back a revenge unit in your hand until your Heroes come back with Destiny, as this will refresh their Revenge, giving them another go around.
On the contrary I think that is one of the reasons it may be a bad play, but more importantly I think I'd generally rather save devour for protecting a Hero or Makto (my version) from silence since that is this deck's one big weakness and devour is your only real out against that. All of your opponent's very best options against an on-board Hero or Makto (silence, madness+sac, touch of the umbren, polymorph, etc) get completely BTFO by a devour, with extra hilarity if you immediately hit the Makto you just sacrificed. I've also devoured for surprise blockers off the top as well. I'm not concerned about this deck in a long game so if I'm not pressed for time I would rather hold out for one of these scenarios.
Let them silence a thing. You have more threats.