Open a model page in the headset browser on Android XR and enter XR from the page. The model is placed in your space and can be inspected there.
Android XR answers the same WebXR immersive-AR session that Meta Quest does, so one URL covers both. On visionOS Safari, which only offers immersive VR, the page falls back to that instead.
No. It is a web page, so the browser is the only thing required.
Only when the source file was authored to scale, and a great many published models are not — in the public catalogue on this site, close to half have a bounding box that cannot be a real object. A size is shown on a model page only where it is believable.