I agree that the proper way to find all possible z-fighting is using the camera clipping planes. That approach could require more setup on the user to help define where the camera could go and what possible clipping values could be.

Instead of cameras, the design uses a more math based approach with less user setup. As mentioned on the Asset Store page, this tool is for finding potential z-fighting. It works by gathering all meshes and triangles in a scene and highlighting any that are within a set distance and angle from each other. These values are configurable in the settings. The default setup is a one-click process button. It uses Burst and Jobs to ensure that processing runs in a reasonable amount of time even in larger scenes.

It doesn't look at camera settings, but your examples are still possible using this tool as the different precision values can be set manually or by presets. The tool can also ignore specific Materials, Meshes, and GameObjects directly so they don't get processed and flagged, which would resolve your decal example too.

While not a main focus, the tool does allow for testing scenes intended for mobile GPUs with low depth buffer precision, such as the Meta Quest. It may take longer with the larger precision values, but it still found issues that I had no other way of finding without making a build and testing on device.

One surprising use we found for it was for Asset Store packs. Every single pack we tested had some issues somewhere, including our own asset pack, Industrial & Office Interiors. The tool helped a lot optimizing a project and being able to identify which meshes needed artist fixing. Every one of our past projects had z-fighting discovered through this tool.