How does the maths work out with Agile attacks?

Basically wondering if someone else has already done the calculations to work out when a lower damage attack with the Agile trait is better than a higher damage attack without it. Is there a good rule of thumb here?

The specific scenario I'm looking at is one of my players' Badger animal companions, which can take 2 actions. If it's in a situation where both those actions are going to be attacks, is it better to bite twice (1d8 without Agile) or bite and then claw (1d6 with Agile). I am mainly wondering about the general rule of thumb though, if there is one.

I'm assuming my reading on the rules here is right. If the first attack is not Agile, but the second one is, that's still only the -4 penalty, right?