JdeBPFortunately today, everything was not as it seemed, and the £30 Integral-branded TF card that I bought from Tesco had *not* in fact failed after a mere 3 hours's use.
It turns out that my cheap and cheerful USB1 card reader, bought on a whim at a computer fair years ago, is a bit crap. I suspect that it's on the border, power-demand wise.
I put the card into a different reader, that has its own PSU, and all of the "device not configured" errors stopped.