All depends on your level of comfort. If you suck at interviews....then any prep course will help build confidence in yourself. Half the battle is knowing what to expect.
Took emerald coast last spring anticipating a Major would call...they didn't and I just recently interviewed with a regional...and yes I would def say it helped me get the job.
Confidence and being personable is really everything.....whatever it takes to be that (if you are not naturally like that) is what I think everyone needs to be. At of the day, they are looking for a dude/dudette they can tolerate on a trip for 3-4 days.