Open the model page in any modern browser and import the .usdz file. It is read and converted to glTF on your own machine, by a USD reader written for this app, and then displayed. No conversion step, no upload, no account.
USDZ has system-level “open and it is in AR” support on iPhone and iPad and nowhere else, which is why the format has a reputation for being Apple-only. It is not: it is a container of USD data, and reading it is something a browser can do.
No. The USDZ is opened and decoded in the browser on your device.
Most do. USD is a large specification and this reader covers the parts that USDZ files in practice use — both the binary crate format and the ASCII one, including meshes whose UV set is not named “st”. A file using something unusual can still fail, and the page will say so rather than showing an empty scene.
The conversion happens in order to display the file. There is no export button today, so treat this as a viewer and inspector rather than a converter.