Buying the FE
For sure, take the FEX or FEJ written if you're applying to the majors, but don't bother with buying the rating. People bought an FE ten years ago, but it really didn't help them even then. In fact, I knew an ERAU instructor (with strange ideas about getting hired) who bought the FE. It didn't help him.
Even ten years ago, not that many people were hiring PFEs, so, I'm sure, fewer still are being hired these days. Moreover, the ones that are hired usually need good panel time to qualify. And, even then, PFEs also needed their A & P.
Hope that helps a little.