What the advantage of a 'bakers couche' for proofing bread and is it safe?
The bakers couche is not just floured fabric, it is usually a hard wearing canvas

It is used to allow the dough to breath, and hold it's shape while your actual bread moulds are being used in the oven. The all over air gap allow the crust to dry slightly. A dry crust  makes it easier to handle and bakes slightly more crispy

The flour is there to stop the soft dough from sticking to the canvas, but a with careful handling and a well worn in couche this should not happen

If you keep the couche dry it should not develop mold or mildew. Even if it does, leave it out in the sunshine, so that the UV light can deal to it. I can't imagine that the occasional normal household mold is going to form dangerous toxins that can survive the oven!

After use, give the couche a good brush down with a clean fine bristled brush, and store somewhere dry

If you have plenty of the fine perforated steel moulds, you wont need to use a couche, just use the pans