It works for both. Without url_stat implemented a warning and symfony error is the result:

- Warning - "Warning: is_file() [<a href='function.is-file'>function.is-file</a>]: Jackalope\BinaryStreamWrapper::url_stat is not implemented! in ../vendor/symfony/symfony/src/Symfony/Component/HttpFoundation/File/File.php on line 40"
- Symfony error: "The file "jackalope://00000000384b19700000000062267418/cms/content/home/additionalInfoBlock/my-slideshow/child_1373829096_112077497/image/jcr:content/jcr:data" does not exist"