How do you create a mirrored 3D part across an angled plane?

[indiancad]

When modelling symmetrical components, the mirror plane is not always parallel to the standard XY, YZ, or XZ planes.

The MIRROR3D command makes this easier by allowing you to define a custom mirror plane using three points.

This is useful when creating matching components for angled brackets, machine parts, or other non-standard shapes.

After mirroring, I also check the position and orientation of the new solid.

Have you used MIRROR3D with a custom plane? What method do you prefer for creating symmetrical 3D parts?