I haven't used anything except Meshy (the free version) and it seemed like it does better with organic things-- cats, people, etc. But I only briefly used it, and not the full paid version. So--I'm not the most experienced but this is my $.02.
What I think you'll get is a complete 3D model generated that you can't really "de construct" or modify easily. Except maybe by cutting it up or something like that. And so far, I see very few AI generated images or models that are perfect. They usually need fixing of some kind.
Moreover--when I design something in 3D, it has assemblies--for example a freight car will have trucks, frame, roof, etc. are all assemblies that can be easily pulled out and modified, and themselves are made of components that can be pulled out and changed. With a solid STL file, you'll have a rough time doing that. I can see using AI to generate the individual parts-- if I can give it a drawing of (lets say) a wheel--then it can generate the wheel component. Then I'll assemble it into the wheelset, then into the trucks, etc.
I suppose at some point you'll be able to ask an AI tool to create a 3D model of a subject--say a station-- and ask it to create individual 3D files for each element-- window, door, roof, etc. I don't think we're quite there yet. Or if we are, it'll be expensive.
