I like the addition of the LGB rear lights and the idea of the metal wheels. I think I am right in saying that they will also give a louder clickety-clack noise over the metal rails.
I am very pleased with the quality of the Playmobil trains, so I added a new car. It is an open freight car, with opening doors. The Playmobil cars are better affordable than the LGB ones
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I have three of the open freight cars like that and I have fitted one with a custom mineral load. Here's a link:
http://www.playmofriends.com/forum/index.php?topic=8045.0An alternative load would be cat litter; glued in place and painted black it will look like coal.
You're right about the cost of LGB rolling stock, plus they are designed as light railway stock and so only have a single, central buffer.