No. "Enter dimensions" lets you specify a rectangle, an L-shape or a free polygon. AR measuring is one way to set the shape, not a requirement.

Treat them as estimates. Check the main edges with a tape measure before ordering, and follow your local building code and the material's own instructions for spacing and sizes.

No. The app counts materials; it does not judge whether your spacing or member sizes are strong enough. Default values are commonly used numbers, not recommendations.

When each row takes a single board there are no joints at all, so the pattern makes no difference. The app says so on screen instead of pretending the choice matters.

Yes. "Save as project" stores it on your device, and you can re-run it later with different specs. Data stays on the device and is never sent anywhere.