We are using the lite version of this plugin on a development site, and have 2 issues:
1) Regardless of what we set in the shortcode, only 4 posts show.
May be there is chance that you have just 4 posts and the load more btn is not visible because there are no more posts to load except those 4. Also, please make sure the category you have selected has more posts.
The posts for the site have been imported from a wordpress.com blog, and we have 92 published posts at the moment. In the settings for the short code (one 1 short code defined at the moment) we have all Categories and all Tags selected. I would therefore expect that all 92 posts should be eligible for display?