Interview prep is as much about how you answer the questions and present yourself as it is about the answers themselves, so the need for that will vary a lot person-to-person. I spent a lot of time getting ready, refining my answers, talking to the mirror, doing a mock interview with my wife (she used to work in HR, so that was a plus!). After all that, I did interview prep at one of the interview companies that frequent APC and quite honestly, it didn't really help much. YMMV. If you think you might need it, it won't hurt. Professional interview prep does not replace your own prep. Feel free to PM me if you want.