After looking at a couple different plans for these, this looks like a nice simple design. There was one set of plans from an older magazine reprint the used two rods, and I never understood why it needed to be more complicated than a single rod design like your's. After looking at this pic, I'd really like to make what you've got.
A few of questions for you...
What's the diameter of the rod you used? (Assuming it needs to be pretty stiff.)
Do you have any ajdustability on the wheels/bearings?
Anything you'd do differently?
Thanks,
Jack