There are several of these metal type bondos you refer to :
All-Metal, Metal-to-Metal & Alumalead.
I havent used them in years .Once it kicks (drying Process) it sands like a piece of granite.

The lite weight fillers used today are way better then years ago,
so dont be afraid of BONDO as it has had a bad rep. Mostly from
not knowing how to mix & use it correctly.

SprayTech