I asked (separately) a number of TREs/TRIs & Training Cpts I work with about doing a JOC earlier this year, and all of them replied that it didn't make any difference to either job prospects with their outfit (actually a 737 EFIS-equipped low-cost operator) or with respect to flying ability. They called it marketing hype on the part of the FTOs and recommended to save the cash for practice sim sessions when you have a confirmed interview; it seems more useful since you can then practice actual sim check ride profiles.
Cheers
