Here is my advice from someone who has been through the process.
If you have been successful in getting an interview, you would have to be nuts not to do interview coaching (FDS/Pinstripe).
This is really a once in a lifetime shot at a decent job. Pay the $500 and come prepared. You would be shocked about how many people on my interview day (~25 people) didn't use it!
It's called 'playing the game'. Good luck all.