Ng-src or $imageCacheFactory for optimizing displayed images?

I have an app that displays menus and items which includes displaying images from external sources.

I have seen conflicting suggestions on how to optimize the display of these images and not sure what to believe at this point.

The two options I am currently battling are:

1. Use $imageCacheFactory https://github.com/andrewmcgivery/ionic-ion-imageCacheFactory to preload images and take advantage of the master-detail pattern.
2. Keep using ng-source because it caches the image.

Are either of these (or both) the correct option? Or is there another way I can optimize displaying external images?