The problem with the composite radiator is NOT the plastic, its the joint between the plastic/metal. The plastic headers are basically crimped on with a seal between the metal/plastic. After some time, expansion/contraction works that joint and it springs a leak. I've actually fixed/reduced a leak or two by squeezing the crimps with a pair of pliers. NOT that I would trust that as a long term fix, but it did get me by for the short term.
So, yes, ALL METAL is the way to go, all metal joined with solder/brazing is far more reliable and stronger than crimping a plastic header on the ends with a gasket.