It integrates an additional option into YouTube videos allowing you to manually adjust the image format by zooming with a slider.
Works well.
If the extension could adjust the formatting itself it would be perfect, but in the meantime it does the job very well and works better than most other extensions I have tried.

Gives me manual control over the zoom unlike any other add-on.

I am missing an automatically inferred zoom, that doesn't necessarily get set without my confirmation, but is rather there as a recommendation with the option to set itself automatically. The algorithm for this should be trivial.