I had two of them. They rattled and popped open on occasion, but it was ~ 15 years ago and Wald may have updated the design. Everything Wald makes is un-pretentious and quite sturdy and I'd have no problem recommending the folding baskets despite my experience.

Instead, I got a fixed basket that I thought was a one-of-a-kind until I saw one last week at my LBS, a Wald 585, for well under 20 bucks. It's just a plain basket. Mine is attached with hose clamps. To further reduce rattling, I put some rolled up pieces of innertube rubber between the basket and my bike rack.

My spouse tried one of these on a seatpost mounted rack, that had side rails for panniers. Nothing kept it from shifting around, or from bending the side rails of the rack under heavy load. She ended up getting a mainstream rack with side stays that go all the way down to the threaded holes on the bottom bracket.

Oh, and I like kickstart's idea.