Has anyone purchased a stroller board to add a rider to your stroller? I have seen a couple of them at Buy Buy Baby and am interested, but the reviews on Amazon aren't very impressive for the Britax one. It's possible that another brand would work with our B-Agile though, I haven't researched it much. Has anyone used one and loved it, or hated it? What age (minimum) do you think a kid would need to be to ride on it safely?

*ETA* This is the kind of thing I'm thinking of:
http://www.amazon.com/Britax-USA-S869800-Stroller-Board/dp/B007CTPX2W
http://www.buybuybaby.com/store/product/Baby-Jogger-reg-Stroller-Glider-Board-Attachment/1016974587