Along the lines of Poacher's Knife right now. Weak and rarely used. What made Devourer strong at release is its base stacks. 45 I believe. It was like 20 less monsters needed to to match the old Devourer. 20. That's a lot of time.
Anyways, here to say that right now it's pretty useless and getting Warrior is much stronger. No point to Devourer.
I've participated in just about every Devourer discussion I've seen on the forums.
It is legitimately by no means weak. If you compare it directly to Feral Flare (which is seen as a largely successful and op item), Devourer gives even more up front damage and stats about ten minutes earlier than Feral Flare. I'll also add that it is incredibly slot efficient, much more than Warrior. This item will be even more relevant at 30m than it was at 10m. The reason why it is believed to be weak is that the scaling is not ensured, because you have to be able to farm your jungle and gank successfully. Due to this, it makes a great snowball item when you're already doing well. Another reason why it's perceived is weak is because the stats it gives are not easily utilized by a lot of junglers.
Off the top of my head, here is a list of junglers that could use Devourer:
AD Alistar Braum (if you're into that, hue) Attack Speed Cho Gangplank Jax Kayle AD Malphite Master Yi Nocturne AD Nunu Olaf Poppy Rek'Sai Rengar Shen Shyvana Skarner Tryndamere Volibear Warwick Xin Zhao
If you look at this list of junglers, most of them are either extremely off meta or can utilize Cinderhulk / Warrior better. There's just not a lot of champions who can utilize that damage properly. I will say that I've played Devourer on quite a few of these champions, and the damage almost always comes around.
Its basically 
only option for the attack speed you need but its very weak. Either improve the base damage or add 10% more attack speed.
In the 4.21 "destroy the wolf" patch theu nerfed Devourer, now its a "Overnerfed" item, maybe need a little buf
ON MAGIC HIT: 25 ---> 30
With that change can put Devourer in a better spot.
