Essentially a training facility with a fairly minimal chance at a job. Supervisors assign projects to postdocs. Many of these projects will be good because they will lead to positive outcomes (publications). However it is not in the supervisor's best interest to assign projects that will lead to the postdoc getting a job for two reasons: The projects main goal is to get the supervisor's grant funded. This may not lead to skills that will be appreciated by future employers in the non-academic world (most likely). Second, if the postdoc is successful the supervisor may want to continue with that line of research, therefor the postdoc may not be able to get funding on that research because the supervisor may submit a competing grant application.
Keep in mind: This is an esteemed institution, but not all primary investigators are particularly good. Some seem to be quite incapable of designing experimental approaches that make much sense. These professors have a tendency to doctor their data. Other's seem to be quite distracted, and aren't following day to day or even week to week research progress and outcomes.
Poor prospects for career development and employment.