I attended one of these last year in London.
Had a chat with the CP and some other hopefuls like myself. They want to get a feel for what is out there it would seem, I never got any thing back from them but then again I found myself on the NS with another company 1 month later. Go figure!
My IR had expired with very limited ME experience, no NS experience.
I am now a true believer in right place right time followed by Who you know not what you know but the latter didn't apply for me.