I got the pedals on the Diamondback and did some riding on them.
I really can't believe how much of a difference there is in feel with the SPD pedals. It really feels like you're part of the bike. It feels more effortless to ride, as well.
I'll definitely be getting a set of those pedals soon for my Bianchi road bike. I'm planning on cleaning the Bianchi up a bit and doing a bit of work to it, so the pedals will be a good thing to replace. It needs new ones anyways.
But anyways...I'm glad I went with the pedals and shoes. The only regret I have about them now is...why didn't I do this sooner???