im just saying that scavenger would be potentially more powerful as it can be triggered several times per turn, devour a max of once and it is a choice and not compulsory. and i wouldnt worry about
adding hp, that would be a trio- assuming devour costs
like scarabs and otys. but with devour being a duo ability, there is no real cost change associated with it (+1 ability, -1 duo ability = 0 net change in card cost). i'd lower the initial hp to 4 so it will tick down to 3 at the start of the turn in which it can use its ability, and it will be limited to eating weak creatures. if nightfall/eclipse it played it would buff the eating ability of the zombie.
but if you dont put devour on it, thats fine, ill see what i can think up for my own card