The older trigger housing was cast aluminum with a black painted finish that would flake off with age. The new plastic part is tougher, stronger and has no paint to flake off.
I have heard the same and actually prefer the polymer trigger housing. One thing I do not prefer is the plastic barrel band, it would constantly come loose after 100 rounds or so. I picked up a couple of the older aluminum barrel bands and stripped the paint off and gave it a brushed finish to match the barrel on my stainless 10/22.