Great plugin

Oh, just one remark.
Your example in the FAQ misses a closing bracket:

<?php
add_filter( 'menu_image_default_sizes', function($sizes){

  // remove the default 36x36 size
  unset($sizes['menu-36x36'];

  // add a new size
  $sizes['menu-50x50'] = array(50,50);

  // return $sizes (required)
  return $sizes;

});
?>

here:

unset($sizes['menu-36x36']);