I was chatting to the Coppers at the Quay last night and have requested details as I am in the risk category: Fairly young, back to biking, not done advanced training etc etc
I have done it and it is a really usefull day out. It makes you take stock of your riding and they give you guidance for minimising the chance of an accident.
I did it in London in December on the Monster. Well worth it, in spite of a slight hiccup in the morning because I didn't take proof of insurance (because they hadn't written to me to ask for it so only took my licence). By the time they got that sorted out I wasn't able to go out on the morning ride, which was annoying but the afternoon was very useful. I think if you learn just one thing that keeps you safer it's worth it. Road positioning was the most helpful thing for me, I think.
Anyway, you've got nothing to lose and possibly something to gain so go with an open mind and positive approach and you'll have a good day.