The only place you can ‘charm’ a carrion devourer is in the Iron Marches.
There is no level restriction for entering IM, but keep in mind the area is rated for levels 50–60. They are found is in a slightly forested plain-type area in the central-south part of the map, so you do need to travel some distance to get one. If you are at a lower level, stay on the roads, evade any encounters, and you might get to one and WP out before something kills you.
As for it being the best ranged pet, it depends on your preferences. The good thing about devourers is that they have a reasonably good AI evade that helps to keep them alive,
Spiders are good ranged pets, but tend to die more often.
I just went to Iron Marches as a level 8, I did not come across 1 Red mob within range from the entrance to the Carrion! It seems game developers planed for it…or not
