upload your own video
custom poster image
custom aspect ratio
the playback rate (speed) is remembered within the website
Summary: the video player will work fine, it's okay to use it.
The app will try to load a script from a remote source, which is not allowed so it will fail. Because of this, you will see an error in the browser console - that's expected, ignore it.
The app uses some variable names (CSS) that are not completely namespaced. It could theoretically have compatibility issues with other packages - though very unlikely. You will most likely not be able to run it on the same page with other video.js based video players.