Jungle main here. I hate it, it's pretty bad. You sacrifice your best moment as a jungle : Early game. This is when you can help your lanes the most. You can easily snowball your lanes, and secure drakes. Devourer don't give a lot of stat early on. You can alway gank early, but you will alway gank less.
It's also more dangerous with devourer, since you are weaker to counter ganks / CCs.
Yes, you deal a bit more damage, but even if it would be a 25% damage increase it would not be worth it (and it's not even close to that). Also, tanks are pretty strong again those AA melee, since you can generaly stunlock them, and give your team enough time to burst that squishy melee in a few seconds.
Basicaly, the item don't make things op, it's just a slight buff to farming jungles. Which hare clear weaknesses.