It would be useful if this plugin had a filter or hook in the 'wp_rss_img_url()' function which could allow developers to add more ways in which an image might appear in relation to a post. There are tons of non-standard ways this happens, such as through hero image plugins, simplefields plugin, or other meta data.
For our use at Sears I've had to make a small edit to the plugin to make it check for meta data generated by using SimpleFields. No big deal but I hate to have to branch other people plugins.
Btw, good job with this plugin. As simple as you would think this is, none of the other plugins supposedly doing this seem to work quite right.