I wanted one of those little wire French racks, so I bought the Dia Compe version only to find I really didn't like it. Too bendy and way too heavy for how tiny it was!
So I tig welded something similar. Like the Dia Compe and TA racks, it only attaches to the brake.
I've carried upwards of 5kg on it, but only for a few miles. My usual bag weighs maybe 2-3kg at its heaviest and that's fine for this. Yes, there's no "strap" to tie into the center mounting bolt. I didn't think it was necessary after seeing how much the Dia Compe rack's strap flexed. I put all the strength in the two brake pivot bolts. The rack itself along with the brake booster plate I made weighs 130g. The brake is heavy, at 190g. I made a whole thread about it -
you can find it here.