Not doing the prep may work out. however out of the 80-90 military applicants I know from the various squadrons I've flown with them in over the years the simple truth is those that didn't do the prep (which was a small number) ended up either not receiving a offer from a Major airline and ended up staying in the military, or adding 6-9 months of additional wait time due to failed interviews / apps not trigging interviews. Most people do not possess enough self-reflection ability to identify if they need interview prep, and honestly, I've wasted far more money on far more questionable endeavors. Adding additional security that you will get both interviewed and pass said interview at a higher rate of success is a simpleton's choice and those choosing not to are not really worth the time helping anyhow.