It also helps Druids or Clerics who picked the Animal domain and I assume oracles as well....True. That wrinkle didn't exist at the time of writing :)Does it actually do that though? Because as it is written, the abilities of your animal companion is treated as if your class were four levels higher to a maximum bonus equal to your character level.
So, as an example a level 6 ranger who has a class level of 6, would have an animal companion that is equal to "effective druid level 3." The feat as its written would boost the ranger level, not the "effective level" which will always be ranger level-3. As a result since the ranger in question is already at maximum class level she would not really benefit from the feat, unles of course she multi-class to another class later.
The same would be applied to druids with the animal domain I presume?
Maximum "bonus" is probably unfortunate wording (not sure if it was in the original draft), but basically, you calculate the abilities of an animal companion or familiar as though your level was four level higher, to a maximum of your actual character level. So a ranger could get the abilities of an animal companion of up to their character level, as opposed to their ranger level - 3. If they've multiclassed, it might still be less than their charater level.
Don't overthink the feat :)
Well, the problem with the feat isn't so much with rangers but its effect on druids who take the animal domain. Correct me if I'm wrong on this, but doesn't it negate most of the reasons for picking an animal companion as a druid? Wouldn't it be much better to just pick the animal domain and pick up this feat? For the druid in question, its effectively picking up a feat for 1 extra spell per spell level. Now, granted if your build is feat intensive that may not be feasible, but generally I think that's something that can be fitted in rather easily, especially since in pathfinder feats are a bit more plentiful. I don't think any of my players who play druids would ever pick an animal companion again, they would all just take the animal domain and pick up this feat, simply because its just that much more economical.