Setting a Content Length of zero for Featured Boxes 2 should cause the excerpt text to disappear, leaving just the title and More link. This doesn’t work. It does work for Featured Boxes (ie the first lot) but not for Featured Boxes 2 (the second lot). It looks like the Content Length is being completely ignored in the second lot.
I cannot confirm this issue, the content length option works fine in my tests (considering the same code is responsible for all featured boxes sections and it cannot behave differently depending on section).
Note however that the option applies to automatically generated excerpts only – manual excerpts defined for posts are always displayed as-is.