They rattle a little. Even if they didn't fold I wouldn't care about a little rattle, though.

But since they do fold flat, I can shove my bike into a packed bike rack at the grocery store and still carry home a load that'll have me in granny gear out of intersections. They'll hold far more than an aluminum rack can carry, I have the evidence. I can carry my bike through the side garage door with me rather than trying to pull it behind me or push it ahead of me. I can put my bike on the front of the bus when the front rim splits ten miles from home, without bogarting the entire rack. They'll never wear out, either; mine are so old they're galvanized instead of painted.

That's worth a little rattle. Folding baskets, ftw.