The Magic Post Thumbnail plugin does not require any special configuration to work properly.
As far as the performance of the plugin on your WordPress is concerned, there will be no impact on the front office of your installation (the part visible to visitors), as the plugin only works in the back office of your WordPress. So there will be no tuning to do with the WordPress caching plugins.
The performance impact on the back office is almost non-existent as the plugin is not very resource intensive. It is only when you generate images that the resources are a bit more demanding, with the API call to your chosen image bank. This generation process can typically take one to a few seconds per image to run and assign the featured image to the page.