Once the add-on has been installed in your WordPress plugins folder and activated through the WordPress administrative interface, a new set of options will appear under Syndication –> Posts & Links, labeled
Limit size of posts. (These settings can be set by creating a global default for all feeds; or they can be set on a feed by feed basis, by using each specific feed’s Posts settings page.)
The options will give you the choice of whether to leave syndicated posts unlimited in length, to cut off syndicated posts after a certain length, or to hide the rest of the post, after a certain length, behind a “Read More…” break.
If you choose to cut off syndicated posts or insert a “Read More…” break, you can choose to limit the length of posts based on:
- Number of characters
- Word count
- Number of sentences
- Break-points from the original source (if the author used them, and the add-on is able to detect them)
If you choose any of the first three options, the add-on will impose a limit after the length you specify. If you choose the last option, it will attempt to find where the original author inserted a “Read More…” break into her article. 
By default, when a post is cut off by the add-on, an ellipsis (
…) will be put at the end of the shortened clip. As an advanced feature, you can actually control and alter the string that appears at the end of a size-limited post. for an illustration of how to do this, see the included
fwplsop-read-more-link.php module, which demonstrates how to change the string from an ellipsis to a link back to the full text of the article at its original source.
-  Of course, not all authors use “Read More…” break-points, and there is no standard way for feeds to indicate where break-points were located on the original source. However, FWP+: Limit Size Of Posts can automatically detect break-points in most feeds produced by popular blogging platforms such as WordPress, Blogger, and LiveJournal. If the add-on fails to find any such break-point, it will fall back on any other length limits (e.g. by word count or number of sentences) that you may have set up. If you prefer for posts only to be broken up where an explicit break-point was set, just select “At Breaks,” and don’t set up any other length limits. ↩