Although I haven't used this app, after reading through the documentation it seems that DJANGO_STATIC_MEDIA_URL is a shortcut to minimize the need to include {{ MEDIA_URL }} when defining the location of your image src attribute.
You define DJANGO_STATIC_MEDIA_URL (www.mysite.com/media), then afterwards you can access the uploaded media's location like
<img src="{% staticfile "/foo.png" %}"/>
Rather than having to write the location as:
<img src="{{ MEDIA_URL }}{% staticfile "/foo.png" %}"/>
So, to reference your css and js static files, continue to use {{ STATIC_URL }}. To reference your uploaded media, either define DJANGO_STATIC_MEDIA_URL and use the {% staticfile %} templatetag only, or just use {{ MEDIA_URL }} as you normally would.