Okay, I'll chime in here in case someone from Lionel, etc. would read this I would not think twice about buying a scale proportioned, nicely detailed plastic steam locomotive. (as in no cast on handrails) The material the "shell" is made of does not matter to me. Of course they would have to put in a weight as the plastic boiler doesn't have the mass those who revel in pulling long trains need.
But a plastic steamer, no problem. Bring 'em on.
