Devourer's Magic Damage on hit
Is it essentially like saying "You have x attack damage" at least in the early game?
Is it essentially like saying "You have x attack damage" at least in the early game?
Eh sort of. It means what it says -- when you attack, you'll deal X magic damage in addition to your attack damage. But it does not count as attack damage for abilities that scale on AD.
Do you think the attackspeed makes up for the loss of damage on towers, and is it a good item on Vi, or does she scale better with AD
It probably depends on your teamcomp and what role you expect to play. I would suspect Vi would work better with AD, but I don't jungle that often so I'm not an expert. People like Sated because of the double on-hit effects, so things like Yi's true damage, TK's % HP on hit, Kayle's shred, Jax's passive, Wit's End, BoTRK, and Cleaver would all benefit from it.
It can work on Vi if you grt ahead, but she really wants to be ganking a lot and sated leans towards farming. If the both teams are fairly tanky and you get ahead it can be pretty good, otherwise cinderhulk or warrior are better. It just depends on if you want burst (warrior), tankiness (cinderhulk), or tank busting (sated).
I'd say, if your team is doing well and doesn't need a ton of ganks, go devo. If they are needing help, go warrior