It's helpful to see it all in one place and be able to iterate with it independently of implementation. It's good at asking questions, then whipping up various options of designs that you can compare side-by-side.

I'm not sure if it's faster or if there's anything different about that model. Like Design and Code might both use raw Opus so we're doing the same thing. Ideally it would be fine-tuned towards design, but to be honest it isn't amazing yet (I'd give it a 6.5/10 as the project grows larger) so I doubt it.