The one-on-one phone call interview prep and the practice run through of all three interviews SWA does the day before my actual interview were invaluable.
I can’t really answer your second question. Would I have gotten the job had I not used them? No idea. I may not have gotten hired if I had different people at SWA interview and ask me different questions that day.
Is it absolutely necessary? Given how laid back the actual interview process is, probably not.
Do I think it was worth my time and money? Without a doubt.