<p>I've read the description of "functionoids" <a href="https://isocpp.org/wiki/faq/pointers-to-members#functionoids" rel="nofollow noreferrer">here</a>. They look like a poor-man's version of Boost::function and Boost::bind. Am I missing something? Is there a good reason to use them if you're already using Boost?</p>

No.
Alternatively see the FQA answer
here.