The early flat metal grills with styro cut inserts were problematic at best. I was told that grill style was discontinued as the magnets rattled and the grills came loose. Just hearsay there, i wasnt around. Then came cloth and of course dome metal. Some were pressure fit as in with the smaller braun bookshelf, some like my 830 there were velcro no longer magnetic. Not sure if cloth vs steel were "optional" but i would gather not. Color/finish was, and perhaps cloth or metal came with a parricular cabinet choice, but likely not as a stand alone option. Stand alone option may have been cost prohibitive do to cab alterations needed to accomodate the 2 styles. Just conjecture on my part, given the rare brochure reading ive done from recollection.
Note: this is in reference to Braun only.