I seriously considered applying for the NIH IRTA program, but in the end I went for research jobs at large universities associated with academic medical centers. I couldn't be happier with my decision. The pay and benefits are better (where I ended up anyway), and I appreciate the vibrancy of university life. It would have been much harder, for instance, for me to continue with my musical studies at the NIH. At a university, it's relatively easy for staff members to join the chorus/knitting club/etc. Most importantly, I'm getting great mentorship at the bench, and I have endless opportunities for clinical exposure over at the hospital.
There are definitely other ways to do research as a postbacc. You don't have to do the NIH IRTA or a specific postbacc program.