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

Treat them as an estimate. Check the main edges with a tape measure before ordering, and follow your local building regulations and the timber merchant's own instructions for spacing and sizes.

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

When one board covers a row there are no joins at all, so the pattern makes no difference. The app shows this on screen rather than pretending it matters.

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