I found the rubnbuff worked well on the grungy oxidised steel fasteners that had given up their cad plated finish. Shock bolts and the like brushed up clean then wiped with the rubnbuff, looked quite good.
Pitted and oxy'd chrome parts looked much better with some RNB.
But after a year or two and rain the oxy is poking back through...
I tried it on aluminum but it looked too fake.