I'm another one who was leery at first, worried about being able to clip out when I needed to. It did take me a while to get past that, but now I wouldn't ride without them. It just doesn't feel comfortable to have my feet "loose". For one thing, I tend to fly off a flat pedal because I'm expecting to stay attached through the top of the stroke. Can be quite unnerving when I want to get off to a quick start at an intersection. Anyway, because it may take a while for you to adjust (or just to decide if you do/don't like them) I might wait til after the Sept ride. Or, as some have suggested, be willing to take the pedals off if you aren't comfortable with them. You certainly don't have to use them, for this ride or ever for that matter. But you might love them!

By the way, I use Candies. I know they're not real road bike pedals but they're simple and consistent to use, and give me just enough platform to pedal on if I don't get clipped in right away at an intersection or just want one foot out for a bit in certain situations.