Union Station Products sides will produce some really fine passenger cars BUT</B> they are Craftsman level kits that require a lot of really careful work.
The sides on a corrugated car, as an example, features no less than three different pieces, not counting the clear backing material that serves as the window glass, two pieces of milled styrene that represent (very accurately) the appropriate corrugation for whatever builder the car represents, and a third piece, which comprises the wall section and the window openings. These pieces must be assembled carefully for it to turn out right and then you have to paint them before gluing them in the clear piece.
The owner of U.S.P. is a great guy and is proud of the work that he does on his car sides. And he has good reason to be proud. As I say, the kits do make some really fine cars, including a large number of cars that will never be made as ready to run models or even as kits or brass car sides. But they are very labour intense compared to other kit types of cars.