Guys, I know that I am overly hung up on nomenclature, but that said, lets for the sake of discussion use the correct terms. The part that holds the trigger, hammer and the other assemblies is called the TRIGGER PLATE. Regardless of the material of it's construction (polymer or aluminum) the assemblies within the trigger plate are bushed with steel cylinders called (pivot tubes) these are the bearing surfaces that the other steel parts ride in and on. In my mind trigger plates of both materials have held up very well in testing and extended use. You can change out the trigger plate to what ever flavor you prefer, however I do not see this as an upgrade, it doesn't make the gun operate any better.
Good Luck & Be Safe