I have two problems with excerpts in your, otherwise, very nice plugin:
1. A real bug, I think: If the number of words in the blog excerpt is smaller than the excerpt_length setting, then the last word in the excerpt is missing in div.slposts-block-excerpt. Add a space at the end of the excerpt text, and the last word is shown. So if you write in your blog the excerpt text 'José Luis', then your plugin shows 'José', but the text 'José Luis ' produces 'José Luis'.
2. More a matter of taste: The setting auto_excerpt=true is fine, but in my view it should *only* create an automatic excerpt if the excerpt in the blog is missing/empty.
Something else: In your installation instructions you mention the Shortcode option values TRUE and FALSE. These do not work; you should use true and false.
Thank you for this plugin; I really appreciate it!!!