I don't know anything about this particular company, but I'm fairly confident I'd have blown my 1st job interview had I not attended Emerald Coast. I don't mean to say ECC has a 100% hire rate and those without interview prep are batting .000 but unless you just know your'e Mr Personality I think it would be a foolish to go in without a little extra help.
If I had a UAL interview it doesn't matter how great a pilot I thought I was, I'd still pony up the cash for a couple hours in the sim prior to the interview. Why wouldn't I get interview prep which applies not only to UAL, but any other airline you might interview with (for ~1/3 the cost of what the sim prep costs)?