Looking for a simple `Filter_classifier` program

Hello list,
    tl;dr: what Filter_classifier do you use, if any?

I filter/delete/highlight messages in my email client (mutt) using simple
regexps like

    =f mergify[bot] !~b \^Merged
        # getmail mergified messages

This is fine but as I add up more regexps, everything becomes slower and
more unwieldy. So I read getmail manual and found `Filter_classifier`.

It seems to do what I want but each example I find on the Internet is about
ham/spam, while I am looking for something slightly different (classifying
some messages in different categories).

I am sure I am not the first getmail user to try this, so I am asking you:
do you know/use any similar program (simple, deals with regexps, outputs a
string)?

Thanks in advance
—F